Don't stop a waveform simply by calling pinMode (esp8266#4906)

Setting a pin direction would cause a waveform generator attached to it to stop.
This could cause PWM to stop if pinMode() is called while running (as it was
called in __analogWrite()).

Remove the stopWaveform call from pinMode, the Tone, analogWrite, or Servo
that initiated the waveform has responsibility for stopping it (and it does)
when complete, irrespective of the pinMode.

Fixes esp8266#4905

cores/esp8266/core_esp8266_wiring_digital.c

@@ -29,7 +29,6 @@
 uint8_t esp8266_gpioToFn[16] = {0x34, 0x18, 0x38, 0x14, 0x3C, 0x40, 0x1C, 0x20, 0x24, 0x28, 0x2C, 0x30, 0x04, 0x08, 0x0C, 0x10};
 
 extern void __pinMode(uint8_t pin, uint8_t mode) {
-  stopWaveform(pin);
   if(pin < 16){
     if(mode == SPECIAL){
       GPC(pin) = (GPC(pin) & (0xF << GPCI)); //SOURCE(GPIO) | DRIVER(NORMAL) | INT_TYPE(UNCHANGED) | WAKEUP_ENABLE(DISABLED)