PSRAM fix not needed for M5 stack core2 (#676)

since all m5 stack core 2 have a actual PSRAM bug free version

Author: Jason2866

boards/m5stack-core2.json

@@ -5,7 +5,7 @@
       "partitions": "default_16MB.csv"
     },
     "core": "esp32",
-    "extra_flags": "-DARDUINO_M5STACK_Core2 -DBOARD_HAS_PSRAM -mfix-esp32-psram-cache-issue",
+    "extra_flags": "-DARDUINO_M5STACK_Core2 -DBOARD_HAS_PSRAM",
     "f_cpu": "240000000L",
     "f_flash": "40000000L",
     "flash_mode": "dio",