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/
BROADWAY_TESTS = [
'text_buffer',
]
TEST_WRAPPER = find_program('./test-wrapper.py', required: true)
BROADWAYD = find_program('gtk4-broadwayd', required: false)
testenv.set('XDG_CONFIG_HOME', meson.current_build_dir() / 'config')
if BROADWAYD.found()
foreach program : BROADWAY_TESTS
e = executable(f'test_@program@', f'test_@program@.c',
c_args : ['-DTEST_DATA_DIR="@0@/data"'.format(meson.current_source_dir()),
'-DTEST_CACHE_DIR="@0@/cache"'.format(meson.current_build_dir())],
dependencies : [libpurple_dep, libpidgin_dep, glib, gtk])
test(program, TEST_WRAPPER,
args : [BROADWAYD.full_path(), e],
is_parallel : false,
env: testenv)
endforeach
endif