cpplint.py: disable obsolete warnings for c++11 and c++14 features

[dconeybe]

This PR removes c++11 and c++14 lint checks, as the floor is c++14 (and has been for almost 2 years, since the merge of #10651). cpplint.py appears to have been written pre-c++11 and has not been updated to fully accept c++11 and c++14 features.

This change will improve the readability of code in this repo by removing the need to unnecessarily sprinkle comments like // NOLINT(build/c++11) all over the place.

This PR makes the following changes to cpplint.py:

• Removes all checks for "approved" c++11 and c++14 headers; all such headers are now "approved".
• Relaxes the prohibition of using namespace declarations to allow for such declarations for the purpose of bringing custom literals into scope, a case where using namespace declarations are generally accepted.
• Removes usage of the obsolete-and-soon-to-be-deleted sre_compile Python module.

#no-changelog