gstreamer: Remove unused function
gstreamer: Remove unused function

rate_control_is_active() is static and not used in gstreamer-encoder.c

Not needed since 97fcad82eb7d1f3bbd8d1163801b5a3db92944c2.

Acked-by: Pavel Grunt <fbda40b445316123f12a5a6bd7556918ea74f4bc@redhat.com>

fgouget/spice,fgouget/spice,fgouget/spice,fgouget/spice