pidgin/purple-plugin-pack

Remove plugin_pack.spec.in as we haven't provided rpms in a long time

Testing Done:
Ran `ninja dist` and verified no issues.

Reviewed at https://reviews.imfreedom.org/r/2404/
if TYPES.contains('default') and PURPLE.found() and IS_PURPLE_TWO
translate = shared_library('translate',
'translate.c',
dependencies : [PURPLE, GLIB],
name_prefix : '',
install : true,
install_dir : PURPLE_LIBDIR)
PP_PURPLE_BUILD += 'translate'
endif