nohz: Remove obsolete check for full dynticks CPUs to be RCU nocbs

Building full dynticks now implies that all CPUs are forced
into RCU nocb mode through CONFIG_RCU_NOCB_CPU_ALL.

The dynamic check has become useless.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Borislav Petkov <bp@alien8.de>