avcodec/libx264: Don't use init_static_data for newer versions

avcodec/libx264: Don't use init_static_data for newer versions

x264 versions >= 153 can support multiple bitdepths; they also don't
export x264_bit_depth any more. The actual check whether a bitdepth
is supported is therefore performed at runtime in x264_encoder_open.
Ergo it is unnecessary to use init_static_data for these versions:
One can already set ff_libx264_encoder.pix_fmts to the value that
X264_init_static always sets it to.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>