memory: remove stray Serial objects

Author: facchinm

cores/arduino/SerialObj2.cpp

@@ -2,16 +2,4 @@
 
 #if SERIAL_HOWMANY > 1
 UART _UART2_(UART2_TX_PIN, UART2_RX_PIN);
-#endif
-
-#if SERIAL_HOWMANY > 2
-UART _UART3_(UART3_TX_PIN, UART3_RX_PIN);
-#endif
-
-#if SERIAL_HOWMANY > 3
-UART _UART4_(UART4_TX_PIN, UART4_RX_PIN);
-#endif
-
-#if SERIAL_HOWMANY > 4
-UART _UART5_(UART5_TX_PIN, UART5_RX_PIN);
 #endif