remove file-as-block device option without envie customizations

Author: pennam

mbed_app.json

@@ -62,7 +62,6 @@
             "mcuboot.scratch-size": "0x20000",
             "mcuboot.max-img-sectors": "0x180",
             "mcuboot.max-align": 32,
-            "mcuboot.file-as-blockdevice": true,
             "mcuboot.mcuboot-as-envie": true,
             "mcuboot.mcuboot-envie-littlefs": true,
             "mcuboot.mcuboot-envie-sdcard": true,