Fix use of \pdfinfo (refs #3551, #3567)

Although the data in ``\pdfinfo`` as set-up in ``sphinxmanual.cls`` was
ignored, some LaTeX commands (e.g. ``\large``) in the ``latex_documents``
title item could cause failed PDF builds.

This commit removes the anyhow ignored ``\pdfinfo`` usage, and indicates
in commented-out lines how to use ``\hypersetup``, which may be done in
master branch, or possibly in stable branch, if some consensus emerges
about how to represent ``\and`` in the ``/Author`` field. It seems the
PDF Document Information Dictionary does not seem to provide any
universal multi-lingual way to indicate multiple authors.

CHANGES

@@ -35,6 +35,8 @@ Bugs fixed
 * #3575: Problems with pdflatex in a Turkish document built with sphinx has
   reappeared (refs #2997, #2397)
 * #3577: Fix intersphinx debug tool
+* A LaTeX command such as ``\\large`` inserted in the title items of
+  :confval:`latex_documents` causes failed PDF build (refs #3551, #3567)
 
 Testing
 --------

sphinx/texinputs/sphinxhowto.cls

@@ -33,15 +33,8 @@
   \noindent\rule{\textwidth}{1pt}\ifsphinxpdfoutput\newline\null\fi\par
   \ifsphinxpdfoutput
     \begingroup
-    % These \defs are required to deal with multi-line authors; it
-    % changes \\ to ', ' (comma-space), making it pass muster for
-    % generating document info in the PDF file.
-    \def\\{, }%
-    \def\and{and }%
-    \pdfinfo{
-      /Author (\@author)
-      /Title (\@title)
-    }%
+     %\pdfstringdefDisableCommands{\def\\{, }\def\endgraf{ }\def\and{, }}%
+     %\hypersetup{pdfauthor={\@author}, pdftitle={\@title}}%
     \endgroup
   \fi
   \begin{flushright}

sphinx/texinputs/sphinxmanual.cls

@@ -43,15 +43,8 @@
     \noindent\rule{\textwidth}{1pt}\ifsphinxpdfoutput\newline\null\fi\par
     \ifsphinxpdfoutput
       \begingroup
-      % These \defs are required to deal with multi-line authors; it
-      % changes \\ to ', ' (comma-space), making it pass muster for
-      % generating document info in the PDF file.
-      \def\\{, }%
-      \def\and{and }%
-      \pdfinfo{
-        /Author (\@author)
-        /Title (\@title)
-      }%
+       %\pdfstringdefDisableCommands{\def\\{, }\def\endgraf{ }\def\and{, }}%
+       %\hypersetup{pdfauthor={\@author}, pdftitle={\@title}}%
       \endgroup
     \fi
     \begin{flushright}%