Cleanup texmanager.

- remove check for "old" cache (the location changed in efa9ea6 (2005)).
- postscriptd and pscnt are unused since c0d6110 (2006), deprecate them.
- make_ps and make_ps_bbox are unused since 310e707 (2009), deprecate
  them.
- calling \usepackage more than once with the same package does nothing
  (as a repeated import in Python) so no need to remove calls to
  \usepackage{type1cm}.
- replace DEBUG by _log.debug where appropriate; other cases (forcing
  file regeneration) can be handled by manually deleting the old file.

Various other minor cleanups.

lib/matplotlib/backends/backend_pdf.py

@@ -686,8 +686,8 @@ def dviFontName(self, dvifont):
         psfont = self.texFontMap[dvifont.texname]
         if psfont.filename is None:
             raise ValueError(
-                ("No usable font file found for {0} (TeX: {1}). "
-                 "The font may lack a Type-1 version.")
+                "No usable font file found for {} (TeX: {}); "
+                "the font may lack a Type-1 version"
                 .format(psfont.psname, dvifont.texname))
 
         pdfname = Name('F%d' % self.nextFont)