Revert "Amend merged PR#2736 to maintain strict stability of pdf title page"

This reverts commit 7db8141238.

As discussed at

<https://github.com/sphinx-doc/sphinx/pull/2736#issuecomment-230140016>

platex and xelatex engines led to a slightly different title page layout
missing a blank line underneath the top rule (above the logo) compared
to pdflatex and lualatex. This was probably accidental.

sphinx/texinputs/sphinxhowto.cls

@@ -30,7 +30,7 @@
 % ``Bjarne'' style a bit better.
 %
 \renewcommand{\maketitle}{%
-  \noindent\rule{\textwidth}{1pt}\ifsphinxpdfoutput\newline\null\fi\par
+  \noindent\rule{\textwidth}{1pt}\newline\null\par
   \ifsphinxpdfoutput
     \begingroup
     % These \defs are required to deal with multi-line authors; it

sphinx/texinputs/sphinxmanual.cls

@@ -40,7 +40,7 @@
   \begin{titlepage}%
     \let\footnotesize\small
     \let\footnoterule\relax
-    \noindent\rule{\textwidth}{1pt}\ifsphinxpdfoutput\newline\null\fi\par
+    \noindent\rule{\textwidth}{1pt}\newline\null\par
     \ifsphinxpdfoutput
       \begingroup
       % These \defs are required to deal with multi-line authors; it