backend_wx: delete remaining lines for removal of printer support

This just finishes off the process; most of the removal was done
in #84ffb60.
Merge pull request #3839 from efiring/wx_printer_last_deletion

backend_wx: delete remaining lines for removal of printer support
Allow style.use() to accept RcParams instances.
Remove isinstance() calls in mpl.styles.use().
Add unit test for style.context() using a dict.
PEP 8.
Update docstring for style.use() and style.context().
Add more informative unit test names. Style cleanup.
Use table for docstring.
Reset style values on any error.
Fixing "line too long (80 > 79 characters)". :-/
Missing import for SkipTest.
Merge pull request #3795 from chebee7i/style-rcparams

ENH : RcParams/dict as input to matplotlib.style.use
wrong method name

wrong method name in docs and abstract class method, simple rename
Merge pull request #3846 from ariejdl/master

BUG : fix typo in base-class MathtextBackend

ABC has class that is never over-ridden by sub-classes and never used, renamed to the method used by sub-classes.
BUG: ensure integer shape, strides for as_strided
Merge pull request #3845 from mbyt/out_of_memory_access_as_strided

BUG: ensure integer shape, strides for as_strided
Added missing implementation of get_window_extent for AxisImage and test (fixes #2980).
Reduce linewidth for PEP-8 compliance.
Split long line.