Remove memoffset dependency from rustc_query_impl.

The comment explains it's for `unstable_offset_of`, but `offset_of` is
now stable.

Author: nnethercote

Cargo.lock

@@ -4412,7 +4412,6 @@ version = "0.0.0"
 dependencies = [
  "field-offset",
  "measureme",
- "memoffset",
  "rustc-rayon-core",
  "rustc_data_structures",
  "rustc_errors",

compiler/rustc_query_impl/Cargo.toml

@@ -22,8 +22,5 @@ rustc_span = { path = "../rustc_span" }
 thin-vec = "0.2.12"
 tracing = "0.1"
 
-# Not used directly, but included to enable the unstable_offset_of feature
-memoffset = { version = "0.9.0", features = ["unstable_offset_of"] }
-
 [features]
 rustc_use_parallel_compiler = ["rustc-rayon-core", "rustc_query_system/rustc_use_parallel_compiler"]