tools: do not link against unused libraries.

tools: do not link against unused libraries.

A fair few things under tools link against libraries which they don't
even use.

Most of this appears to come from copy-and-pasting previous Makefile
snippets and cargo-culting plus the tendency to define global $(LIBS)
even for Makefiles which build multiple separate utilities or
libraries.

Identified by comparing a build with --as-needed to one without by
looking at the NEEDED header of all ELF objects.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>