FAT: Removed implicit MBR from FAT filesystem during format

- Implicit MBR still allowed during mount
  - maintains storage compatibility
- Not needed
  - MBR utility is not exposed through the FAT filesystem,
    so the only used partition was always the first. Omitting
    the MBR is functionally equivalent
  - Saves a few blocks on storage for MBR + offset
    for FAT alignment
- Duplicated with MBRBlockDevice
  - The implicit MBR actually prevents nesting a FAT filesystem
    in the MBRBlockDevice

features/filesystem/fat/FATFileSystem.cpp

@@ -290,7 +290,7 @@ int FATFileSystem::format(BlockDevice *bd, int allocation_unit) {
 
     // Logical drive number, Partitioning rule, Allocation unit size (bytes per cluster)
     fs.lock();
-    FRESULT res = f_mkfs(fs._fsid, 0, allocation_unit);
+    FRESULT res = f_mkfs(fs._fsid, 1, allocation_unit);
     fs.unlock();
     if (res != FR_OK) {
         return fat_error_remap(res);