grim/pidgin

Remove the GtkAlignment from PidginCredentialsPage as it's deprecated.

Testing Done:
Compiled and ran locally. Note that glade 3.38 doesn't show the margin on load, but if you tweak the value you'll see that it does work.

Reviewed at https://reviews.imfreedom.org/r/484/
libpurple/data/purple-url-handler.desktop.in
libpurple/protocols/null/nullprpl.c
pidgin/data/im.pidgin.Pidgin.desktop.in
sub/libpurple/data/purple-url-handler.desktop.in
sub/libpurple/protocols/null/nullprpl.c
sub/pidgin/data/im.pidgin.Pidgin.desktop.in