avformat/movenc: only ommit encoder tag of the metadata for bitexact mode

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/movenc: omit LIBAVCODEC_IDENT for bitexact mode from uuidusmt_tag

This code is apparently not tested by fate

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avformat/movenc: omit avformat ident from isml_manifest for bitexact mode

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