hv_ename_delete should not delete the HvNAME

hv_ename_delete should not delete the HvNAME

This is something that 78b79c7758 missed.

When xhv_name is a HEK *, it is both the regular name and the effect-
ive name at the same time. Only when xhv_name_count is negative is the
regular name not also the effective name.

hv_ename_delete needs to take the HEK that xhv_name points to and
put it in a new HEK * array in xhv_name. This array will just have
one element.

When xhv_name_count is negative, effective names start with the second
element. So we set xhv_name_count to -1 so there isn’t one.