pidgin/pidgin

Remove PurplePluginAction as everything except finch as been ported to GAction/GMenu.

The finch buddy list code has just been #if 0'd for the time being.

Testing Done:
Compiled and greped for `"actions-cb"` to make sure no plugins were still using the property.

Reviewed at https://reviews.imfreedom.org/r/1755/
if libsecret.found()
libsecret_plugin = library('libsecret', 'libsecret.c',
c_args : ['-DG_LOG_USE_STRUCTURED', '-DG_LOG_DOMAIN="Purple-LibSecret"'],
dependencies : [libsecret, libpurple_dep],
name_prefix : '',
install : true, install_dir : PURPLE_PLUGINDIR)
devenv.append('PURPLE_PLUGIN_PATH', meson.current_build_dir())
endif