MKSHARE=no blows up build in mozilla-rootcerts

With MKSHARE=no there's no "clean" target in the mozilla-rootcerts
Makefile, and a non-update build splodes.  Perhaps nobody else cares,
but I thought I should note it for posterity.  I'll fix it in due course
after I find more stuff that blows up with MKXYZ=no set (that is, I'll
gather the changes and make them all at once for cleanliness).

-- 
Thor Lancelot Simon	                                     [email protected]
  "The liberties...lose much of their value whenever those who have greater
   private means are permitted to use their advantages to control the course
   of public debate."					-John Rawls