Add comment after #endif for "Conditional" for consistency

Every "Conditional" #endif have following "// ENABLE(ConditionXXX)"
except for place registering function callback.
This patch fix it so that we can use a common routine
to generate #endif for "Conditional" in python generator.

This patch also remove unused code.

R=haraken@chromium.org
BUG=239771
TEST=TestInterface.idl, TestObject.idl

Review URL: https://chromiumcodereview.appspot.com/19511003

git-svn-id: svn://svn.chromium.org/blink/trunk@154367 bbb929c8-8fbe-4397-9dbb-9b2b20218538