html: Remove cosmetic whitespace inside p tags

All tags are put on a line by themselves to help with visual
diffing. Apparently this extra cosmetic whitespace causes problems inside p
tags for ppl who want to use `white-space: pre`. Not much hurt for visual
diffing in removing cosmetic whitespace for just p tags and can't think of
anything that would break because of this right now. So let's do it and wait
for things to break.

org/testdata/latex.html

@@ -1,43 +1,27 @@
-<p>
-without latex delimiters the <code class="verbatim">_{i=1}</code> in <code class="verbatim">\sum_{i=1}^n a_n</code> is interpreted as subscript.
-we support <code class="verbatim">\(...\)</code>, <code class="verbatim">\[...\]</code>, <code class="verbatim">$$...$$</code> and <code class="verbatim">\begin{$env}...\end{$env}</code> as latex fragment delimiters.
-</p>
+<p>without latex delimiters the <code class="verbatim">_{i=1}</code> in <code class="verbatim">\sum_{i=1}^n a_n</code> is interpreted as subscript.
+we support <code class="verbatim">\(...\)</code>, <code class="verbatim">\[...\]</code>, <code class="verbatim">$$...$$</code> and <code class="verbatim">\begin{$env}...\end{$env}</code> as latex fragment delimiters.</p>
 <ul>
 <li>
-<p>
-∑<sub>i=1</sub>^n a_n (without latex delimiter)
-</p>
+<p>∑<sub>i=1</sub>^n a_n (without latex delimiter)</p>
 </li>
 <li>
-<p>
-\(\sum_{i=1}^n a_n\)
-</p>
+<p>\(\sum_{i=1}^n a_n\)</p>
 </li>
 <li>
-<p>
-\[\sum_{i=1}^n a_n\]
-</p>
+<p>\[\sum_{i=1}^n a_n\]</p>
 </li>
 <li>
-<p>
-$$\sum_{i=1}^n a_n$$
-</p>
+<p>$$\sum_{i=1}^n a_n$$</p>
 </li>
 <li>
-<p>
-\begin{xyz}\sum_{i=1}^n a_n\end{xyz}
-</p>
+<p>\begin{xyz}\sum_{i=1}^n a_n\end{xyz}</p>
 </li>
 <li>
-<p>
-\begin{xyz}
+<p>\begin{xyz}
 \sum_{i=1}^n a_n
-\end{xyz}
-</p>
+\end{xyz}</p>
 </li>
 <li>
-<p>
-$2 + 2$, $3 - 3$
-</p>
+<p>$2 + 2$, $3 - 3$</p>
 </li>
 </ul>