Rollup merge of #93431 - lqd:remove-jemallocator, r=Mark-Simulacrum

remove unused `jemallocator` crate

When it was noticed that the rustc binary wasn't actually using jemalloc via `#[global_allocator]` and that was removed, the dependency remained.

Tests pass locally with a `jemalloc = true` build, but I'll trigger a try build to ensure I haven't missed an edge-case somewhere.

r? ```@ghost``` until that completes

Cargo.lock

@@ -3319,7 +3319,6 @@ dependencies = [
  "rustc_codegen_ssa",
  "rustc_driver",
  "tikv-jemalloc-sys",
- "tikv-jemallocator",
 ]
 
 [[package]]
@@ -5164,16 +5163,6 @@ dependencies = [
  "libc",
 ]
 
-[[package]]
-name = "tikv-jemallocator"
-version = "0.4.1"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3c14a5a604eb8715bc5785018a37d00739b180bcf609916ddf4393d33d49ccdf"
-dependencies = [
- "libc",
- "tikv-jemalloc-sys",
-]
-
 [[package]]
 name = "time"
 version = "0.1.43"