Remove redundant setting of pg_attribute.attcompression

Since e6241d8e0, no attribute needs a non-default value of this during
initdb, so let the usual machinery for defaults take care of it.

src/backend/catalog/genbki.pl

@@ -905,7 +905,6 @@ sub morph_row_for_pgattr
 	$row->{attbyval}       = $type->{typbyval};
 	$row->{attalign}       = $type->{typalign};
 	$row->{attstorage}     = $type->{typstorage};
-	$row->{attcompression} = '\0';
 
 	# set attndims if it's an array type
 	$row->{attndims} = $type->{typcategory} eq 'A' ? '1' : '0';