Prune rustc dependencies.

Cargo.lock

@@ -3111,8 +3111,6 @@ dependencies = [
  "bitflags",
  "byteorder",
  "chalk-engine",
- "fmt_macros",
- "graphviz",
  "jobserver",
  "log",
  "measureme",

src/librustc/Cargo.toml

@@ -12,8 +12,6 @@ doctest = false
 [dependencies]
 arena = { path = "../libarena" }
 bitflags = "1.2.1"
-fmt_macros = { path = "../libfmt_macros" }
-graphviz = { path = "../libgraphviz" }
 jobserver = "0.1"
 scoped-tls = "1.0"
 log = { version = "0.4", features = ["release_max_level_info", "std"] }