tools/flask/utils: remove unused variables/targets from Makefile

tools/flask/utils: remove unused variables/targets from Makefile

They are no *.opic or *.so in this subdir, so no need to clean them.

The TEST* variables doesn't seems to be used anywhere, and they weren't
used by xen.git when introduced.
Both CLIENTS_* variables aren't used.
Both target "print-dir" and "print-end" only exist in this directory
and are probably not used anywhere.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>
[Drop trailing whitespace and use $(RM) consistently]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>