MFC r351799, r351816: NOP; these two revert each other

r351799:
LOCAL_MODULES: Allow LOCAL_MODULES="" in src.conf to work

Currently LOCAL_MODULES= works, but LOCAL_MODULES="" causes build errors as
.for still has the empty string to loop over. An .if empty prior to the loop
was considered, but LOCAL_MODULES has empty quotes at that point and thus,
isn't empty. A better solution likely exists, but this floats us by for
now...

r351816:
Back out r351799

empty does not appear to work like I thought it did and it actively breaks
real LOCAL_MODULES usage, of which I have none at the moment...