Remove useless bms_copy step in RelationGetIndexAttrBitmap.
Seems to be from a bad case of copy-and-paste-itis in commit
665d1fad9.
It wouldn't be quite so annoying if it didn't contradict the comment
half a dozen lines above.
David Rowley
Discussion: https://postgr.es/m/CAKJS1f95Dyf8Qkdz4W+PbCmT-HTb54tkqUCC8isa2RVgSJ_pXQ@mail.gmail.com