Fully remove submodule handling from bootstrap.py

These submodules were previously updated in python because Cargo gives a hard error if toml files
are missing from the workspace:

```
error: failed to load manifest for workspace member `/home/jnelson/rust-lang/rust/src/tools/rls`

Caused by:
  failed to read `/home/jnelson/rust-lang/rust/src/tools/rls/Cargo.toml`

Caused by:
  No such file or directory (os error 2)
failed to run: /home/jnelson/rust-lang/rust/build/x86_64-unknown-linux-gnu/stage0/bin/cargo build --manifest-path /home/jnelson/rust-lang/rust/src/bootstrap/Cargo.toml
```

However, bootstrap doesn't actually need to be part of the workspace.
Remove it so we can move submodule handling fully to Rust, avoiding duplicate code between Rust and Python.

Note that this does break `cargo run`; it has to be `cd src/bootstrap && cargo run` now.
Given that we're planning to make the main entrypoint a shell script (or rust binary),
I think this is a good tradeoff for reduced complexity in bootstrap.py.

Author: jyn514

Cargo.lock

@@ -215,32 +215,6 @@ dependencies = [
  "byte-tools",
 ]
 
-[[package]]
-name = "bootstrap"
-version = "0.0.0"
-dependencies = [
- "cc",
- "cmake",
- "filetime",
- "getopts",
- "hex 0.4.2",
- "ignore",
- "libc",
- "num_cpus",
- "once_cell",
- "opener",
- "pretty_assertions 0.7.2",
- "serde",
- "serde_json",
- "sha2",
- "sysinfo",
- "tar",
- "toml",
- "walkdir",
- "winapi",
- "xz2",
-]
-
 [[package]]
 name = "bstr"
 version = "0.2.13"
@@ -735,15 +709,6 @@ dependencies = [
  "rustc-semver",
 ]
 
-[[package]]
-name = "cmake"
-version = "0.1.44"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0e56268c17a6248366d66d4a47a3381369d068cce8409bb1716ed77ea32163bb"
-dependencies = [
- "cc",
-]
-
 [[package]]
 name = "colored"
 version = "2.0.0"
@@ -1023,9 +988,9 @@ dependencies = [
 
 [[package]]
 name = "ctor"
-version = "0.1.15"
+version = "0.1.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "39858aa5bac06462d4dd4b9164848eb81ffc4aa5c479746393598fd193afa227"
+checksum = "f877be4f7c9f246b183111634f75baa039715e3f46ce860677d3b19a69fb229c"
 dependencies = [
  "quote",
  "syn",
@@ -2670,9 +2635,9 @@ checksum = "8e22443d1643a904602595ba1cd8f7d896afe56d26712531c5ff73a15b2fbf64"
 
 [[package]]
 name = "output_vt100"
-version = "0.1.2"
+version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "53cdc5b785b7a58c5aad8216b3dfa114df64b0b06ae6e1501cef91df2fbdf8f9"
+checksum = "628223faebab4e3e40667ee0b2336d34a5b960ff60ea743ddfdbcf7770bcfb66"
 dependencies = [
  "winapi",
 ]
@@ -2931,18 +2896,6 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "925383efa346730478fb4838dbe9137d2a47675ad789c546d150a6e1dd4ab31c"
 
-[[package]]
-name = "pretty_assertions"
-version = "0.7.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1cab0e7c02cf376875e9335e0ba1da535775beb5450d21e1dffca068818ed98b"
-dependencies = [
- "ansi_term",
- "ctor",
- "diff",
- "output_vt100",
-]
-
 [[package]]
 name = "pretty_assertions"
 version = "1.2.1"
@@ -5147,21 +5100,6 @@ dependencies = [
  "unicode-xid",
 ]
 
-[[package]]
-name = "sysinfo"
-version = "0.24.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a6a8e71535da31837213ac114531d31def75d7aebd133264e420a3451fa7f703"
-dependencies = [
- "cfg-if 1.0.0",
- "core-foundation-sys",
- "libc",
- "ntapi",
- "once_cell",
- "rayon",
- "winapi",
-]
-
 [[package]]
 name = "tar"
 version = "0.4.38"
@@ -5538,7 +5476,7 @@ dependencies = [
  "colored",
  "crossbeam",
  "lazy_static",
- "pretty_assertions 1.2.1",
+ "pretty_assertions",
  "regex",
  "rustc_version",
  "serde",

Cargo.toml

@@ -1,7 +1,5 @@
 [workspace]
-default-members = ["src/bootstrap"]
 members = [
-  "src/bootstrap",
   "compiler/rustc",
   "library/std",
   "library/test",
@@ -44,6 +42,7 @@ exclude = [
   "build",
   "compiler/rustc_codegen_cranelift",
   "compiler/rustc_codegen_gcc",
+  "src/bootstrap",
   "src/test/rustdoc-gui",
   # HACK(eddyb) This hardcodes the fact that our CI uses `/checkout/obj`.
   "obj",
@@ -97,15 +96,6 @@ gimli.debug = 0
 miniz_oxide.debug = 0
 object.debug = 0
 
-# The only package that ever uses debug builds is bootstrap.
-# We care a lot about bootstrap's compile times, so don't include debug info for
-# dependencies, only bootstrap itself.
-[profile.dev]
-debug = 0
-[profile.dev.package]
-# Only use debuginfo=1 to further reduce compile times.
-bootstrap.debug = 1
-
 # We want the RLS to use the version of Cargo that we've got vendored in this
 # repository to ensure that the same exact version of Cargo is used by both the
 # RLS and the Cargo binary itself. The RLS depends on Cargo as a git repository