Remove indentation from <programlisting> blocks in docs

Remove indentation from <programlisting> blocks in docs

Many dozens (hundreds?) of documentation code blocks were indented to
match the surrounding XML or just arbitrarily. The thing is: Inside
<programlisting> tags, similar to <pre> tags, line feeds and leading
whitespace are being preserved, which looked very awkward in the HTML
documentation. While a few files were mostly correct in this respect,
which shows that it was meant to be like that, many others were not.
This was tedious, stupid work to fix, but it had to be done.

Please note that the documentation was in no way updated content-wise.
This is also overdue, but not my focus here.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>