configure.ac: remove detection of chcon
configure.ac: remove detection of chcon

caf88b55568150e8a7b0eccbd82b6fe9ed93c2f1 removed the last user of this,
but forgot to clean up configure.ac.

martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,cockpit-project/cockpit