pidgin/pidgin

Remove a number of functions from gtkconv.c and gtkconvwin.c that aren't used anymore

Testing Done:
Compile only

Reviewed at https://reviews.imfreedom.org/r/907/
NULL_SOURCES = [
'nullprpl.h',
'nullprpl.c'
]
# nullprpl isn't built by default; when it is built, it's dynamically linked
if DYNAMIC_NULL
null_prpl = shared_library('null', NULL_SOURCES,
dependencies : [libpurple_dep, glib],
install : false, install_dir : PURPLE_PLUGINDIR)
endif