Revert "Reenable opt-level 3"

This reverts commit 30383b2.

Author: Mark-Simulacrum

src/Cargo.toml

@@ -18,6 +18,14 @@ members = [
   "tools/rls",
 ]
 
+# Curiously, compiletest will segfault if compiled with opt-level=3 on 64-bit
+# MSVC when running the compile-fail test suite when a should-fail test panics.
+# But hey if this is removed and it gets past the bots, sounds good to me.
+[profile.release]
+opt-level = 2
+[profile.bench]
+opt-level = 2
+
 # These options are controlled from our rustc wrapper script, so turn them off
 # here and have them controlled elsewhere.
 [profile.dev]