Remove all compat-* functions in Stylus

The compat-* functions were used to override styles from the old design.
The functions used !important to do this. By removing the functions and
the associated use of !important, our stylesheets will be more
maintainable and reliable. This also reduces the size of compiled CSS by
2.04KB.

Some bugs were fixed just by removing these functions. At the same time,
some bugs were revealed by removing these functions. (For example,
errors related to selector specificity suddenly manifested as
user-facing bugs when !important was removed.)

Newly-manifesting bugs like these were searched for and corrected, but
it is possible that some remain. If we find any more, we can correct
them with later commits.
Merge pull request #2401 from openjck/remove-compat

Remove all compat-* functions in Stylus