Consolidate IDL test cases (15%: 34 => 29)

This consolidates the test cases post-rewrite.

Specifically:
* Remove old Perl TestInterface and TestObject (-2 files)
* Move special operations into TestInterface{,2,3} (-2 files)
(2 TestSpecialOperations*.idl left b/c 5 variants total, if squeezed so overlap)
* Remove TestEventTarget, as covered by TestInterfaceEventTarget (-1 file)
* Rename s/(.*)Python.idl/\1.idl

TBR=haraken
BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/213543004

git-svn-id: svn://svn.chromium.org/blink/trunk@170287 bbb929c8-8fbe-4397-9dbb-9b2b20218538