package/netsniff-ng: Fix build caused by extra 'install' target

package/netsniff-ng: Fix build caused by extra 'install' target

After commit:

	b0f98d5 package/netsniff-ng: allow to build with uclibc but w/o mausezahn

the different build and install targets are specified depending if
masuezahn tool is able to be selected or not. It works for the build
case but for the install the old 'install' target was not removed from
the make invocation and it still forces to install the mausezahn, so fix
it by remove this target.

Fixes:
	http://autobuild.buildroot.net/results/cc44ed737799c9ac73628c82b86bd526b1c43310/
	http://autobuild.buildroot.net/results/72d0753532720604d51c05663af7fbfe37434339/

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>