grim/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/
subdir('bonjour')
subdir('facebook')
subdir('gg')
subdir('irc')
subdir('jabber')
subdir('novell')
subdir('null')
subdir('sametime')
subdir('silc')
subdir('zephyr')