rmdir Source/core/mathml and move SVG .in files.

This directory was essentially empty already. It just contained two "names"
files that were used by the HTML parser. This CL moves those names files into
the HTML parser directory.

I've also renamed the files to be consistent with other "names" files and
to remove some special cases in the build system. I wasn't able to completely
remove the "attr.in" special case because it's still used by a few other files.

R=eseidel

Review URL: https://chromiumcodereview.appspot.com/23530075

git-svn-id: svn://svn.chromium.org/blink/trunk@158227 bbb929c8-8fbe-4397-9dbb-9b2b20218538