Remove redundant entries from genfs_contexts.

I572ea22253e0c1e42065fbd1d2fd7845de06fceb introduced a whitelist, so
everything under tracing/ is assumed to be debugfs_tracing_debug
unless explicitly marked as debugfs_tracing.

Test: Device boots, labels under /sys/kernel/debug/tracing are unchanged.
Change-Id: Id0f0cbcc9e5540551bd2906fbf75f8e939dc4d4c