I would also leave the lug in place, for the following reasons, it is a shame to cut original BSA parts up, it has had a different brake fitted already so not original for your bike, is not doing any harm, does not look awful, also at some stage you may decide to revert to original and then the fork leg would be available to some one else also looking for original fork legs for their model, these usable spares are becoming more difficult/expensive to source.
Just my 2p worth