Fix m5stack_core_esp32 related board variants (#290)

* In the espressif/arduino-esp32 repository the variant m5stack_core_esp32 was renamed to m5stack_core.
See espressif/arduino-esp32@a1c86ae#diff-498a5473e69c1931584e14350d29bc3f8b22f7cf7469d3ef81c896298c9f9291
Therefore some m5stack boards were updated correspondingly.

* Remove ldscript configuration from M5Stack JSON

Removed Arduino ldscript configuration from build settings.

* Remove ldscript configuration from m5stack-core-esp32

Removed Arduino ldscript configuration from build settings.

* Remove ldscript configuration from m5stack-grey.json

Removed Arduino ldscript configuration from build settings.

---------

Co-authored-by: Jason2866 <24528715+Jason2866@users.noreply.github.com>

Author: BlueAndi

boards/m5stack-core-esp32-16M.json

@@ -1,15 +1,12 @@
 {
   "build": {
-    "arduino":{
-      "ldscript": "esp32_out.ld"
-    },
     "core": "esp32",
-    "extra_flags": "-DARDUINO_M5Stack_Core_ESP32",
+    "extra_flags": "-DARDUINO_M5Stack_Core",
     "f_cpu": "240000000L",
     "f_flash": "80000000L",
     "flash_mode": "qio",
     "mcu": "esp32",
-    "variant": "m5stack_core_esp32"
+    "variant": "m5stack_core"
   },
   "connectivity": [
     "wifi",

boards/m5stack-core-esp32.json

@@ -1,15 +1,12 @@
 {
   "build": {
-    "arduino":{
-      "ldscript": "esp32_out.ld"
-    },
     "core": "esp32",
-    "extra_flags": "-DARDUINO_M5Stack_Core_ESP32",
+    "extra_flags": "-DARDUINO_M5Stack_Core",
     "f_cpu": "240000000L",
     "f_flash": "80000000L",
     "flash_mode": "qio",
     "mcu": "esp32",
-    "variant": "m5stack_core_esp32"
+    "variant": "m5stack_core"
   },
   "connectivity": [
     "wifi",

boards/m5stack-grey.json

@@ -1,15 +1,12 @@
 {
   "build": {
-    "arduino":{
-      "ldscript": "esp32_out.ld"
-    },
     "core": "esp32",
-    "extra_flags": "-DARDUINO_M5Stack_Core_ESP32",
+    "extra_flags": "-DARDUINO_M5Stack_Core",
     "f_cpu": "240000000L",
     "f_flash": "40000000L",
     "flash_mode": "dio",
     "mcu": "esp32",
-    "variant": "m5stack_core_esp32"
+    "variant": "m5stack_core"
   },
   "connectivity": [
     "wifi",