ext4: remove redundant checks of s_encoding

Now that ext4 does not allow inodes with the casefold flag to be
instantiated when unsupported, it's unnecessary to repeatedly check for
support later on during random filesystem operations.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230814182903.37267-3-ebiggers@kernel.org


Signed-off-by: Theodore Ts'o <tytso@mit.edu>