Remove unneeded dependencies from rustc_monomorphize.

Author: nnethercote

Cargo.lock

@@ -4293,7 +4293,6 @@ dependencies = [
  "rustc_errors",
  "rustc_fluent_macro",
  "rustc_hir",
- "rustc_index",
  "rustc_macros",
  "rustc_middle",
  "rustc_session",

compiler/rustc_monomorphize/Cargo.toml

@@ -13,7 +13,6 @@ rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
-rustc_index = { path = "../rustc_index" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_middle = { path = "../rustc_middle" }
 rustc_session = { path = "../rustc_session" }