STM32: F2: adc; struct member not needed

Same as other families applied here

Author: LMESTM

targets/TARGET_STM/TARGET_STM32F2/objects.h

@@ -55,7 +55,6 @@ struct port_s {
 };
 
 struct analogin_s {
-    ADCName adc;
     ADC_HandleTypeDef handle;
     PinName pin;
     uint8_t channel;