mkrevision.mk: Remove Make workaround
mkrevision.mk: Remove Make workaround

- Remove workaround for rule generation ordering issues in newer versions of
GNU Make.  revision.c is generated via a proper rule now, so the workaround
is no longer necessary.

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr