Reduce bicycle spawn frequency somewhat

Based on PR feedback from other devs/players, I'm dialing back the
bicycle spawn frequency significantly from my previous commit.

The total adjustment now is that bicycles are roughly 1.5 - 2 times as
likely to appear in city streets, suburban homes, and parking lots, as
they are in the current experimental branch.

Adjustments made in this commit include:

In "city_vehicles" (i.e. in streets everywhere):

- "bicycle" weight is 800 (originally 400), making them
  rarer than "car", "car_hatch", "ambulance", or "hippie_van",
  but more likely than "beetle", "car_mini", "bus", "rv", or "4x4_car".
  Same chance of spawning as a "pickup" or "suv".

- "bicycle_dirt" weight is 200 (originally 0, impossible), making them
  as likely as "suv_electric", "motorcycle", "truck_swat", or "fire_engine"

- "bicycle_electric" weight is back to 100 (originally 100)

In "suburban_home":

- "bicycle" weight is now 200 (originally 150),
  same chance as "4x4_car" or "motorcycle"

- "bicycle_dirt" weight is now 150 (originally 125),
  same chance as "car_anmlcmpt"

And in "parkinglot":

- "bicycle" weight left at 1000 (originally 500)

- "bicycle_dirt" removed again (back how it was before)

Partially fixes #37451

data/json/vehicle_groups.json

@@ -14,9 +14,9 @@
       [ "suv_electric", 120 ],
       [ "car_mini", 400 ],
       [ "beetle", 500 ],
-      [ "bicycle", 2000 ],
-      [ "bicycle_dirt", 1000 ],
-      [ "bicycle_electric", 500 ],
+      [ "bicycle", 800 ],
+      [ "bicycle_dirt", 200 ],
+      [ "bicycle_electric", 100 ],
       [ "motorcycle", 200 ],
       [ "motorcycle_cross", 20 ],
       [ "motorcycle_enduro", 50 ],
@@ -166,8 +166,8 @@
       [ "suv_electric", 120 ],
       [ "pickup", 300 ],
       [ "portable_generator", 50 ],
-      [ "bicycle", 1000 ],
-      [ "bicycle_dirt", 500 ],
+      [ "bicycle", 200 ],
+      [ "bicycle_dirt", 150 ],
       [ "bicycle_electric", 100 ],
       [ "tricycle", 5 ],
       [ "4x4_car", 200 ]
@@ -216,7 +216,6 @@
       [ "bicycle", 1000 ],
       [ "rara_x", 300 ],
       [ "unicycle", 100 ],
-      [ "bicycle_dirt", 500 ],
       [ "bicycle_electric", 200 ],
       [ "motorcycle", 500 ],
       [ "superbike", 50 ],