Remove unused Polynomials constant from root_locus.jl

Author: baggepinnen

lib/ControlSystemsBase/src/root_locus.jl

@@ -1,4 +1,3 @@
-const Polynomials = ControlSystemsBase.Polynomials
 import ControlSystemsBase.RootLocusResult
 @userplot Rlocusplot
 
@@ -309,4 +308,4 @@ Plot the root locus of the LTISystem `P` as computed by `rlocus`.
     else
         rlocus(p.args[1]; K=K)
     end
-end
+end