Don't include outer join relids in lateral_relids bitmapsets.

Don't include outer join relids in lateral_relids bitmapsets.

This avoids an assertion failure when outer joins are rearranged
per identity 3.  Listing only the baserels from a PlaceHolderVar's
ph_lateral set should be enough to ensure that the required values
are available when we need to compute the PHV --- it's what we
did before inventing nullingrel sets, after all.  It's a bit
unsatisfying; but with beta2 hard upon us, there's not time to
look for an aesthetically cleaner fix.

Richard Guo and Tom Lane

Discussion: https://postgr.es/m/CAMbWs48Jcw-NvnxT23WiHP324wG44DvzcH1j4hc0Zn+3sR9cfg@mail.gmail.com