Revert "cpupower Makefile change to help run the tool without 'make install'"

This reverts commit 5c1de006.

While the original commit makes it easier to run cpupower from the
local build directory, it also leaves the binary with a rather poor
rpath of './' in it after it is installed on a system via 'make install'.

This is considered bad practice and can cause cpupower to fail in
rpmbuild with the following error:

ERROR   0004: file '/usr/bin/cpupower' contains an insecure rpath './' in [./]
error: Bad exit status from /var/tmp/rpm-tmp.A6u26r (%install)
    Bad exit status from /var/tmp/rpm-tmp.A6u26r (%install)

Developers should be able to use LD_LIBRARY_PATH to achieve the same
effect and not introduce rpath into the binary.

Signed-off-by: Josh Boyer <jwboyer@feoraproject.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>