Don't fix Sphinx regex anymore

I assume it has been fixed on the Sphinx side a long time ago. It was
reported a long time ago anyway.

For #236.

breathe/directives.py

@@ -19,16 +19,12 @@
 from docutils.parsers.rst.directives import unchanged_required, unchanged, flag
 from sphinx.writers.text import TextWriter
 from sphinx.builders.text import TextBuilder
-from sphinx.domains import cpp
 
 import os
 import fnmatch
 import re
 import subprocess
 
-# Somewhat outrageously, reach in and fix a Sphinx regex
-cpp._identifier_re = re.compile(r'(~?\b[a-zA-Z_][a-zA-Z0-9_]*)\b')
-
 
 class NoMatchingFunctionError(BreatheError):
     pass