IDL compiler: remove special case for SVGTransformList

Remaining: 1 => 0 (all files identical between Perl and Python)

There's a special case (WTF::getPtr) for one complicate case.
Per Kouhei, this is no longer necessary, so removing.

This finishes the rewrite.
Once everything lands, just need to switch the build with:
IDL compiler: switch build to Python compiler
https://codereview.chromium.org/166333002

BUG=239771
TBR=haraken, kouhei

Review URL: https://codereview.chromium.org/177273002

git-svn-id: svn://svn.chromium.org/blink/trunk@167741 bbb929c8-8fbe-4397-9dbb-9b2b20218538