package/linphone: remove ffmpeg-related patches

package/linphone: remove ffmpeg-related patches

The linphone package never provided video support.

While this commit
https://git.buildroot.net/buildroot/commit/package/linphone?id=dec04466549cd40e2696ae7725e90d6559bee640

added support for ffmpeg 3.0+ the next commit, which fixed the build of
the bundled mediastreamer2 library, added --disable-video:
https://git.buildroot.net/buildroot/commit/package/linphone?id=f3492b28d89c1f2448c9662a6f755cb48e8c0f0b

At this point the ffmpeg 3.0 patches could have been removed because
ffmpeg is only used if video support is enabled:

https://github.com/BelledonneCommunications/mediastreamer2/blob/6c2a608800a221942f2a827e0abb60346e7d065f/acinclude.m4#L80
https://github.com/BelledonneCommunications/mediastreamer2/blob/6c2a608800a221942f2a827e0abb60346e7d065f/acinclude.m4#L107

This patch catches up on that to avoid changing the upstream URL for
the patches which is broken.

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