media_codecs.xml: Remove ffmpeg h263/h264/mp4v-es entries

Codecs covered by OMX.google (and whitelisted by the ffmpeg extractor)
shouldn't be assigned to other software decoders as well

https://github.com/CyanogenMod/android_device_oppo_msm8974-common/commit/507a4c562ce225e1608e577fdc3c443d0e0208c7
https://github.com/CyanogenMod/android_device_oppo_msm8974-common/commit/ce2a426463d0b9057484806fe7db68c3d6eba083