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/
i18n = import('i18n')
i18n.gettext('pidgin',
args : '--from-code=utf-8',
install : get_option('nls'),
)