Remove unneeded check in String::remove(unsigned int)

This check already happens in the remove(unsigned int, unsigned int)
method that is caled, so there is no need to also check this here.

hardware/arduino/avr/cores/arduino/WString.cpp

@@ -684,7 +684,6 @@ void String::replace(const String& find, const String& replace)
 }
 
 void String::remove(unsigned int index){
-	if (index >= len) { return; }
 	int count = len - index;
 	remove(index, count);
 }