radard: remove deprecated function

selfdrive/controls/radard.py

@@ -80,10 +80,6 @@ class Track:
 
     self.cnt += 1
 
-  def get_key_for_cluster(self):
-    # Weigh y higher since radar is inaccurate in this dimension
-    return [self.dRel, self.yRel*2, self.vRel]
-
   def reset_a_lead(self, aLeadK: float, aLeadTau: float):
     self.kf = KF1D([[self.vLead], [aLeadK]], self.K_A, self.K_C, self.K_K)
     self.aLeadK = aLeadK