Remove the obsolete static_branch() interface, since the supported interface
is now static_key_false()/true() - which is used by all in-tree code.

See commit:

  c5905afb ("static keys: Introduce 'struct static_key', static_key_true()/false()
  and static_key_slow_[inc|dec]()").
Signed-off-by: NJason Baron <jbaron@redhat.com>
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/199332c47eef8005d5a5bf1018a80d25929a5746.1340909155.git.jbaron@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>