[partition] Pick slightly more sensible defaults for FS selection

src/modules/partition/partition.conf

@@ -147,7 +147,10 @@ defaultFileSystemType:  "ext4"
 #
 # The value *defaultFileSystemType* is added to this list (with a warning)
 # if not present; the default pick is the *defaultFileSystemType*.
-availableFileSystemTypes:  ["ext4", "btrfs", "f2fs"]
+#
+# If not specified at all, uses *defaultFileSystemType* without a
+# warning (this matches traditional no-choice-available behavior best).
+# availableFileSystemTypes:  ["ext4","f2fs"]
 
 # Show/hide LUKS related functionality in automated partitioning modes.
 # Disable this if you choose not to deploy early unlocking support in GRUB2