mdadm/test: mdadm needn't make install on the system

mdadm/test: mdadm needn't make install on the system

Fixes: beb71de04d31 ("mdadm/test: enable clustermd testing under clustermd_tests/")
clustermd_tests/func.sh:
remove unnecessary 'make install', just ensure 'make everything' has done.
the original idea is to make the /sbin/mdadm version same as ./mdadm, and
this breakage has pointed out by commit:
59416da78fc6 ("tests/func.sh: Fix some total breakage in the test scripts")

Signed-off-by: Zhilong Liu <zlliu@suse.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>