planning: remove deprecated config proto field

modules/planning/conf/planning_config.pb.txt

@@ -102,7 +102,6 @@ em_planner_config {
         max_speed: 20.0
         max_acceleration: 2.5
         max_deceleration: -4.5
-        reference_line_kernel_weight: 0.2
 
         st_boundary_config {
             boundary_buffer: 0.1

modules/planning/proto/qp_spline_st_speed_config.proto

@@ -21,6 +21,5 @@ message QpSplineStSpeedConfig {
   optional double max_speed = 14 [ default = 20.0 ];
   optional double max_acceleration = 15 [ default = 4.5 ];
   optional double max_deceleration = 16 [ default = -4.5 ];
-  optional double reference_line_kernel_weight = 17 [ deprecated = true ];
   optional apollo.planning.StBoundaryConfig st_boundary_config = 18;
 }

modules/planning/testdata/conf/planning_config.pb.txt

@@ -102,7 +102,6 @@ em_planner_config {
         max_speed: 20.0
         max_acceleration: 2.5
         max_deceleration: -4.5
-        reference_line_kernel_weight: 0.2
 
         st_boundary_config {
             boundary_buffer: 0.1