Remove two variables that were not used and caused the following
warnings:

CC      libavformat/mpegtsenc.o
libavformat/mpegtsenc.c: In function 'mpegts_write_section':
libavformat/mpegtsenc.c:72:18: warning: unused variable 'ts'
libavformat/mpegtsenc.c: In function 'mpegts_insert_null_packet':
libavformat/mpegtsenc.c:586:18: warning: unused variable 'ts'
Signed-off-by: Mans Rullgard <mans@mansr.com>
(cherry picked from commit 6e78c8ee)