tracefs: remove stale update_gid code

tracefs: remove stale update_gid code

commit 29142dc92c37d3259a33aef15b03e6ee25b0d188 upstream.

The 'eventfs_update_gid()' function is no longer called, so remove it
(and the helper function it uses).

Link: https://lore.kernel.org/all/CAHk-=wj+DsZZ=2iTUkJ-Nojs9fjYMvPs1NuoM3yK7aTDtJfPYQ@mail.gmail.com/
Fixes: 8186fff7ab64 ("tracefs/eventfs: Use root and instance inodes as default ownership")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>