ima: Remove deprecated IMA_TRUSTED_KEYRING Kconfig

Time to remove "IMA_TRUSTED_KEYRING".

Fixes: f4dc3778

 ("integrity: define '.evm' as a builtin 'trusted' keyring") # v4.5+
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>