package/freerdp: bump version to 2.0.0-rc2

Fixes build with upcoming ffmpeg version 4.0.2.

Removed 0001-Fix-gstreamer-1.0-detection.patch, applied upstream.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>