This fixes #220.

Removing strings from test files is still dangerous, but much
less likely to cause problems after this change to do the
removal after removing comments.

The bug could still manifest if a test file contains defines two
macros, one that contains a single quotation mark and then another
defined somewhere after it that contains a single quotation mark.
Everything in between the aforementioned quotation marks would
still be ignored after this commit, but that is an unlikely
scenario.