Fix misstatement in comment in Makefile.shlib.

Fix misstatement in comment in Makefile.shlib.

There is no need for "all: all-lib" to be placed before inclusion of
Makefile.shlib.  Makefile.global is what ensures that "all" is the
default target, and we already document that that has to be included
first.  Per comment from Pavel Raiskup.

Discussion: <1925924.izSMJEZO3x@unused-4-107.brq.redhat.com>