Make inline "pylint: disable=" notes more clear

Switch ambiguous statements such as "pylint: disable=W0621" with clearer disable statements such as "pylint: disable=redefined-outer-name". I propose that we should be using the clearer form throughout the codebase, so code reviewers know what's going on and coders don't blindly carry over disable statements that no longer apply.

This is also the recommendation made here: https://github.com/edx/edx-platform/blob/master/docs/en_us/developers/source/testing/code-quality.rst
It doesn't need to be, but to be strictly correct, a disable for a chunk of code should be followed by an enable when we're done explicitly disabling the pylint violation. In this file it doesn't matter because it's the end of the code, but (god forbid) more code is added to the file, we would want the violation re-enabled.