[seqfan] easy and bref

[Max Alekseyev]

>From the definition of 'bref' and 'easy' keywords:

bref: Sequence is too short to do any analysis with
easy: It is easy to produce terms of this sequence

it follows that 'easy' sequence cannot be 'bref' (if it is easy to
compute terms of the sequence, we can do any analysis with it).

However, there are currently 24 sequences in the OEIS that are both
'easy' and 'bref'.
Should we drop one of the two keywords must be dropped for each of them.

Regards,
Max