pidgin/pidgin

Move purple_compat_date_time_format_iso8601 to just be a static inline with its normal glib name

Testing Done:
Compiled and ran locally. Also ran `ninja pidgin-pot libpurple-doc`

Reviewed at https://reviews.imfreedom.org/r/633/
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