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/
[main]
host = https://www.transifex.com
[pidgin.pidgin_pot-for-development-branch]
file_filter = po/<lang>.po
source_file = po/pidgin.pot
source_lang = en