libutil++: Move to clibs

This library only installs manual pages, so putting it in its own
package means we build a FreeBSD-libutil++-man package but not a
base FreeBSD-libutil++ package.  Without a base package, the man
package can't be installed due to the missing dependency.

We don't really need a separate package for a few manpages, so move
it to clibs.

Reviewed by:		des
Differential Revision:	https://reviews.freebsd.org/D51756

lib/libutil++/Makefile

@@ -1,4 +1,4 @@
-PACKAGE=	lib${LIB}
+PACKAGE=	clibs
 LIB_CXX=	util++
 INTERNALLIB=	true
 SHLIB_MAJOR=	1

release/packages/ucl/libutil++-all.ucl

@@ -1,4 +0,0 @@
-comment = "C++ utility library"
-desc = <<EOD
-libutil++ contains various C++ utility classes used by the base system.
-EOD