Remove SVGDocument from bindings generator and test cases

Bindings generator side to:
Remove SVGDocument binding
https://codereview.chromium.org/146193003

SVGDocument had hard-coded special treatment in the CG,
so the change to an actual IDL file broke run-bindings-tests.
This is ok (we're not going to run r-b-t on every IDL edit!
and it's easy to fix), but something to be aware of.

BUG=238366
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/151043002

git-svn-id: svn://svn.chromium.org/blink/trunk@166182 bbb929c8-8fbe-4397-9dbb-9b2b20218538