Minor maintenance on pgf docs/backends.

- Remove vague mention of outdated tex packages (first because it was
  written more than 10 years ago so packages too old for backend_pgf
  compatibility are unlikely to be seen nowadays, and second because if
  we don't actually provide compatibility bounds such a statement is not
  particularly useful).
- Fix consistency between xetex/xelatex, and also for capitalization.
- Remove an unnecessary encoding step in PdfPages by directly formatting
  bytes.

Author: anntzer

galleries/users_explain/text/pgf.py

@@ -152,10 +152,6 @@
 Troubleshooting
 ===============
 
-* Please note that the TeX packages found in some Linux distributions and
-  MiKTeX installations are dramatically outdated. Make sure to update your
-  package catalog and upgrade or install a recent TeX distribution.
-
 * On Windows, the :envvar:`PATH` environment variable may need to be modified
   to include the directories containing the latex, dvipng and ghostscript
   executables. See :ref:`environment-variables` and
@@ -175,7 +171,7 @@
 
 * Configuring an ``unicode-math`` environment can be a bit tricky. The
   TeXLive distribution for example provides a set of math fonts which are
-  usually not installed system-wide. XeTeX, unlike LuaLatex, cannot find
+  usually not installed system-wide. XeLaTeX, unlike LuaLaTeX, cannot find
   these fonts by their name, which is why you might have to specify
   ``\setmathfont{xits-math.otf}`` instead of ``\setmathfont{XITS Math}`` or
   alternatively make the fonts available to your OS. See this

lib/matplotlib/backends/backend_pgf.py

@@ -995,14 +995,10 @@ def savefig(self, figure=None, **kwargs):
             # luatex<0.85; they were renamed to \pagewidth and \pageheight
             # on luatex>=0.85.
             self._file.write(
-                (
-                    r'\newpage'
-                    r'\ifdefined\pdfpagewidth\pdfpagewidth'
-                    fr'\else\pagewidth\fi={width}in'
-                    r'\ifdefined\pdfpageheight\pdfpageheight'
-                    fr'\else\pageheight\fi={height}in'
-                    '%%\n'
-                ).encode("ascii")
+                rb'\newpage'
+                rb'\ifdefined\pdfpagewidth\pdfpagewidth\else\pagewidth\fi=%fin'
+                rb'\ifdefined\pdfpageheight\pdfpageheight\else\pageheight\fi=%fin'
+                b'%%\n' % (width, height)
             )
         figure.savefig(self._file, format="pgf", backend="pgf", **kwargs)
         self._n_figures += 1