I'm sure the Python script will work for you. However, it should be easy
enough to select the B alternative positions with "@.b" and then use
"Actions > Atom/Bonds > delete" to wipe them out. Then save the new PDB
file. This will do exactly the same thing as the script you identified and
may be easier for you.

If you want to consider occupancy values, you may have to manually inspect
the PDB file yourself. But maybe Elaine can come up with a clever way to
do that in Chimera...