EXT4_UTIL: remove ext4 flex_bg from default feature

Remove ext4 flex_bg from default feature since vold does not
consider this condition when encrypting /data with FDE.

If not remove flex_bg, /data cannot properly be encrypted.
And some raw data would be corrupt after decrypting.

Bug: 78537335
Test: run encryption/decryption and the data is not corrupt
Change-Id: I62fb8dbdd50036c16a4958bb720c4bfebac88e93
diff --git a/ext4_utils/mke2fs.conf b/ext4_utils/mke2fs.conf
index db77173..abf0dae 100644
--- a/ext4_utils/mke2fs.conf
+++ b/ext4_utils/mke2fs.conf
@@ -12,7 +12,7 @@
         features = has_journal
     }
     ext4 = {
-        features = has_journal,extent,huge_file,flex_bg,dir_nlink,extra_isize,uninit_bg
+        features = has_journal,extent,huge_file,dir_nlink,extra_isize,uninit_bg
         inode_size = 256
     }
     ext4dev = {