objtool: Remove btrfs_assertfail() from the noreturn exceptions list

The objtool merge in commit 6f612579 ("Merge tag 'objtool-core ...")
generated a semantic conflict that was not resolved.

The btrfs_assertfail() entry was removed from the noreturn list in
commit b831306b ("btrfs: print assertion failure report and stack
trace from the same line") because btrfs_assertfail() was changed from a
noreturn function into a macro.

The noreturn list was then moved from check.c to noreturns.h in commit
6245ce4a ("objtool: Move noreturn function list to separate file"),
and should be removed from that post-merge as well.

Do it explicitly.

Cc: David Sterba <dsterba@suse.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>