Auto merge of #45446 - leodasvacas:remove-libcollections, r=alexcrichton

Remove deprecated `collections` crate.

The real `collections` was merged with `alloc`, this facade was introduced [in this PR](#42720) to give `#[no_std]` users time to adapt. This was done at least two cycles ago, now we can consider removing it for good.

Author: bors

src/Cargo.lock

@@ -738,7 +738,6 @@ impl Step for Src {
             "src/liballoc_jemalloc",
             "src/liballoc_system",
             "src/libbacktrace",
-            "src/libcollections",
             "src/libcompiler_builtins",
             "src/libcore",
             "src/liblibc",

src/bootstrap/dist.rs

@@ -490,7 +490,7 @@ impl Step for Std {
         // for which docs must be built.
         if !build.config.compiler_docs {
             cargo.arg("--no-deps");
-            for krate in &["alloc", "collections", "core", "std", "std_unicode"] {
+            for krate in &["alloc", "core", "std", "std_unicode"] {
                 cargo.arg("-p").arg(krate);
                 // Create all crate output directories first to make sure rustdoc uses
                 // relative links.

src/bootstrap/doc.rs

@@ -15,7 +15,6 @@ alloc_jemalloc = { path = "../liballoc_jemalloc", optional = true }
 alloc_system = { path = "../liballoc_system" }
 panic_unwind = { path = "../libpanic_unwind", optional = true }
 panic_abort = { path = "../libpanic_abort" }
-collections = { path = "../libcollections" }
 core = { path = "../libcore" }
 libc = { path = "../rustc/libc_shim" }
 rand = { path = "../librand" }