manpage-normal.xsl: fold in manpage-base.xsl

manpage-normal.xsl: fold in manpage-base.xsl

After an earlier commit, we only include manpage-base.xsl from a single
file, manpage-normal.xsl. Fold the former into the latter.

We only ever needed the "base, normal and non-normal" construct to
support a single non-normal case, namely to work around issues with
docbook-xsl 1.72 handling backslashes and dots. If we ever need
something like this again, we can re-introduce manpage-base.xsl and
friends. Whatever issue we'd be trying to work around, it probably
wouldn't involve dots and backslashes like this, anyway.

Signed-off-by: Martin Ågren <redacted>
Signed-off-by: Junio C Hamano <redacted>