IDL compiler: Remove TestInterfaceImplementedAs.idl

TestInterfaceImplementedAs.idl is not needed, as it is covered by
TestInterfacePython.idl (which has [ImplementedAs]).
This CL removes it.

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/130043003

git-svn-id: svn://svn.chromium.org/blink/trunk@164721 bbb929c8-8fbe-4397-9dbb-9b2b20218538