stm32/boards/NUCLEO_L073RZ: Skip board-pin names for CPU only pins.

This board doesn't have much flash and removing these unneeded names saves
about 900 bytes of code size.

ports/stm32/boards/NUCLEO_L073RZ/pins.csv

@@ -33,55 +33,55 @@ SWDIO,PA13
 SWCLK,PA14
 USER_B1,PC13
 LED_GREEN,PA5
-PA0,PA0
-PA1,PA1
-PA2,PA2
-PA3,PA3
-PA4,PA4
-PA5,PA5
-PA6,PA6
-PA7,PA7
-PA8,PA8
-PA9,PA9
-PA10,PA10
-PA11,PA11
-PA12,PA12
-PA13,PA13
-PA14,PA14
-PA15,PA15
-PB0,PB0
-PB1,PB1
-PB2,PB2
-PB3,PB3
-PB4,PB4
-PB5,PB5
-PB6,PB6
-PB7,PB7
-PB8,PB8
-PB9,PB9
-PB10,PB10
-PB11,PB11
-PB12,PB12
-PB13,PB13
-PB14,PB14
-PB15,PB15
-PC0,PC0
-PC1,PC1
-PC2,PC2
-PC3,PC3
-PC4,PC4
-PC5,PC5
-PC6,PC6
-PC7,PC7
-PC8,PC8
-PC9,PC9
-PC10,PC10
-PC11,PC11
-PC12,PC12
-PC13,PC13
-PC14,PC14
-PC15,PC15
-PD2,PD2
-PF0,PF0
-PF1,PF1
-PF11,PF11
+,PA0
+,PA1
+,PA2
+,PA3
+,PA4
+,PA5
+,PA6
+,PA7
+,PA8
+,PA9
+,PA10
+,PA11
+,PA12
+,PA13
+,PA14
+,PA15
+,PB0
+,PB1
+,PB2
+,PB3
+,PB4
+,PB5
+,PB6
+,PB7
+,PB8
+,PB9
+,PB10
+,PB11
+,PB12
+,PB13
+,PB14
+,PB15
+,PC0
+,PC1
+,PC2
+,PC3
+,PC4
+,PC5
+,PC6
+,PC7
+,PC8
+,PC9
+,PC10
+,PC11
+,PC12
+,PC13
+,PC14
+,PC15
+,PD2
+,PF0
+,PF1
+,PF11