This reverts commit f23016c9.

this attribute is mandatory as per the XEP.

DIGEST and HMAC were static variables. Those are initialized by
what ever concrete implementation gets executed first.

(Perform SCRAM-SHA1 first and those variables got initialized with
SHA1 variants)

For subsequent SHA256 executions those variables contained wrong
values.

after removing the ability to select and copy text the transformation methods
provided by CopyTextView are no longer necessary.

fixes #3940

maybe fixes #3924

note that the ROMs I tested this on don’t require scanning for it
to appear on MTP. However it certainly don’t hurt either.