Remove uses of rules_cc (#776)

Per https://github.com/bazelbuild/rules_cc this still isn't necessary. There's no build-time enforcement, so usage is inconsistent/incorrect. Rather than letting this linger, remove it pending Bazel tooling enforcing it.

executable_semantics/ast/BUILD

@@ -2,8 +2,6 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-load("@rules_cc//cc:defs.bzl", "cc_library")
-
 package(default_visibility = ["//executable_semantics:__subpackages__"])
 
 cc_library(