tools: fix uninstall: tests/x86_emulator, Linux hotplug

tools: fix uninstall: tests/x86_emulator, Linux hotplug

Fixing top-level "make uninstall":

tools/tests/x86_emulator is missing an uninstall target, which causes
failure. Trivial to add one since it installs nothing, so do that.

Linux hotplug uninstall returns success but doesn't actually remove what
it installed. The Makefile variables are obfuscating incorrect logic, so
strip them out and match existing code for xen-watchdog which does work.

Signed-off-by: Christopher Clark <christopher.clark6@baesystems.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>