Cleanup: Remove some unused functions. (#11429)

These were picked up with cppcheck.

Codechange: pass "ground vehicle" to GetTileSlopeZ since for tunnel/bridges there are two states

Previously it checked the position in non-driving direction to "guess" whether
a ground vehicle was using the function, so on tunnels/bridges it could either
return the Z of the (virtual) ground compared to the Z of the path the vehicle
would take.

Fix #8123: trams on half-tiles couldn't find depots (#8738)

Basically, follow_track.hpp contains a fix for half-tiles, but
this wasn't duplicated for when trying to find a depot and in
a few other places. This makes sure all places act the same.

Fix: [YAPF] Road pathfinder did not account for length of tunnel/bridge in path cost

Copy calculations from the rail pathfinder

Fix #7592: Do not cache road vehicle path within 8 tiles of destination with multiple entrances

Ported from jgrpp commit 79d5be7e265df3be8b73d484f0c7261b3c23229d

(svn r18404) -Codechange: link drive through stops better together
-Feature: make penalty for road stop occupancy user configurable
-Fix [FS#1944]: road vehicles would not pick an empty drive through stop. Now they will *if* the penalty for driving around is less than the occupancy penalty
-Fix [FS#1495]: long (articulated) road vehicles could block loading of others when the following road vehicle already got 'permission' to go to the next bay even when it could not reach it
-Change: improve the throughput of the drive through road stops by letting them stop closer together