remove NRF52840, NRF52832 static_memory_defines set

static_memory_defines controls the macro MBED_RAM_START AND MBED_RAM_SIZE
when nrf52840 to use softdevice, it need MBED_RAM_START to set the true application ram start

default static_memory_defines is true, so just remove NRF52840 and NRF52832's set

Author: woodsking2

targets/targets.json

@@ -7219,7 +7219,6 @@
     "MCU_NRF52832": {
         "inherits": ["Target"],
         "core": "Cortex-M4F",
-        "static_memory_defines": true,
         "macros": [
             "BOARD_PCA10040",
             "NRF52",
@@ -7376,7 +7375,6 @@
         "inherits": ["Target"],
         "components_add": ["QSPIF"],
         "core": "Cortex-M4F",
-        "static_memory_defines": false,
         "macros": [
             "BOARD_PCA10056",
             "NRF52840_XXAA",