Remove output fps flag

Apparently, ffmpeg's x11grab device automatically handles
duplication without saying so in the output.

ffmpeg -f x11grab -framerate 60 [...] -vcodec libx264 out.avi
results in a 60fps file with 60*duration frames even if the input
is a lower framerate (IE: my system gets 40fps from x11grab, the
device will duplicate frames it misses to reach 60fps input, and
the output will naturally match the input at 60fps)
Shorter codec option format