IDL compiler: Fix re in Perl IDL compiler

The re in IsCallbackInterface was too loose, resulting in incorrect
test results for test files that use TestObject,
since it accidentally matches a comment.
This re has been tightened up in compute_dependencies.py
(add a '{' at the end), so it already works correctly in Python;
this syncs Perl.

TBR=haraken

Review URL: https://codereview.chromium.org/142703004

git-svn-id: svn://svn.chromium.org/blink/trunk@165396 bbb929c8-8fbe-4397-9dbb-9b2b20218538