hevc: always clip luma_log2_weight_denom

Its value shall be between 0 and 7 according to the specifications.

CC: libav-stable@libav.org
Bug-Id: CID 1257502
mpegvideo: remove unused function declaration
mpegvideo: move REBASE_PICTURE where it is used

Drop an unused #undef from h264 decoder.
Merge commit 'b2bece5e9a4dd96142962c6798e187c77b88bbfa'

* commit 'b2bece5e9a4dd96142962c6798e187c77b88bbfa':
  hevc: always clip luma_log2_weight_denom

Merged-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/hevc: Print an error if luma_log2_weight_denom is out of range

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '63fcedcf01247f15b72c0d1f959bb3b612853ba8'

* commit '63fcedcf01247f15b72c0d1f959bb3b612853ba8':
  mpegvideo: remove unused function declaration

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'd75190aa93206c02cb4f18a66d2c927d6a0198e1'

* commit 'd75190aa93206c02cb4f18a66d2c927d6a0198e1':
  mpegvideo: move REBASE_PICTURE where it is used

Merged-by: Michael Niedermayer <michaelni@gmx.at>