Revert change to delay from last commit

Further testing after including python wrapper indicates the original
delay seems to be about this best its going to get as far as a
compromise between delaying a bit/throughput and reliability of payloads
when rapidly switching between modes.

RF24.cpp

@@ -735,9 +735,7 @@ void RF24::startListening(void)
   }
 
   // Go!
-  #if defined (RF24_LINUX) || defined (__arm__)
   delayMicroseconds(100);
-  #endif
   listeningStarted = 1;
 }