pidgin/pidgin

Remove duplicate private headers variable, and fix corresponding license headers

The duplicate variable was limiting which files were being checked for license headers in the test.

Testing Done:
Ran `ninja turtles`.

Reviewed at https://reviews.imfreedom.org/r/2964/
syntax: glob
.*.swp
.DS_Store
.flatpak-builder
*.pyc
*~
\#*\#
syntax: regexp
^build(.+)?\/
win32-install-dir(\.release)?
po\/pidgin3\.pot$
^subprojects\/.+\/