IDL compiler: remove empty statement from void methods

Noticed another case of blank lines in void methods when implementing
optional arguments; this fixes it in Perl,
and means we can skip it in Python.

Followup to:
IDL compiler: remove blank line for void methods
https://codereview.chromium.org/48003002/

BUG=239771

Review URL: https://codereview.chromium.org/49163006

git-svn-id: svn://svn.chromium.org/blink/trunk@160807 bbb929c8-8fbe-4397-9dbb-9b2b20218538