Remove deprecated collections crate.

This reverts commit 6484258.

Author: leoyvens

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

@@ -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" }