FIX: remove cwd from mac font path search

While including the cwd makes sense at first glance, it does not
because

a) the result is cached so the next time your cwd will be
   different but we will not find those files
b) the time it takes to search all the files is causing prolems
c) the other 2 platforms do not do this

The comma was introduced to fix what looked like a bug (implicit
string concatenation instead of adding the empty string to the list)
in #11963.

Original code come in via 4799341 in
2011.

closes #12176

lib/matplotlib/font_manager.py

@@ -129,7 +129,6 @@
     "/System/Library/Fonts/",
     # fonts installed via MacPorts
     "/opt/local/share/fonts",
-    "",
 ]
 
 if not USE_FONTCONFIG and sys.platform != 'win32':