Clean up board definition to conform to the target spec

Author: drewcassidy

targets/targets.json

@@ -3760,16 +3760,9 @@
     },
     "OSHCHIP": {
         "inherits": ["MCU_NRF51_32K_UNIFIED"],
-        "extra_labels_add": ["OSHCHIP"],
-        "macros_add": ["TARGET_OSHCHIP" , "TARGET_NRF_LFCLK_RC"],
         "device_has": ["ANALOGIN", "I2C", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "SLEEP", "SPI", "SPI_ASYNCH", "SPISLAVE"],
-        "release_versions": ["2", "5"],
-        "device_name": "nRF51822_xxAA",
-        "config": {
-            "lf_clock_src": {
-                "value": "NRF_LF_SRC_RC",
-                "macro_name": "MBED_CONF_NORDIC_NRF_LF_CLOCK_SRC"
-            }
+        "overrides": {
+            "target.lf_clock_src": "NRF_LF_SRC_RC"
         }
     }
 }