[clang-tidy] Fix a few more issues in google-readability-casting

* suggest static_cast instead of reinterpret_cast for casts from void*
* top-level const doesn't need a const_cast
* don't emit a separate "possibly redundant cast" warning, instead suggest
  static_cast (in C++ only) and add a little hint to consider removing the cast

llvm-svn: 296753