fscrypt: remove unnecessary calls to fscrypt_require_key()

fscrypt: remove unnecessary calls to fscrypt_require_key()

In an encrypted directory, a regular dentry (one that doesn't have the
no-key name flag) can only be created if the directory's encryption key
is available.

Therefore the calls to fscrypt_require_key() in __fscrypt_prepare_link()
and __fscrypt_prepare_rename() are unnecessary, as these functions
already check that the dentries they're given aren't no-key names.

Remove these unnecessary calls to fscrypt_require_key().

Link: https://lore.kernel.org/r/20201118075609.120337-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>