Clean Up Unused Travel Modes

[daniel-j-h]

Looking over supported travel modes in #2877 I came across unused travel modes:

osrm-backend/include/extractor/travel_mode.hpp

Lines 49 to 54 in b285835

	// FIXME only for testbot.lua
	const constexpr osrm::extractor::TravelMode TRAVEL_MODE_STEPS_UP = 8;
	const constexpr osrm::extractor::TravelMode TRAVEL_MODE_STEPS_DOWN = 9;
	const constexpr osrm::extractor::TravelMode TRAVEL_MODE_RIVER_UP = 10;
	const constexpr osrm::extractor::TravelMode TRAVEL_MODE_RIVER_DOWN = 11;
	const constexpr osrm::extractor::TravelMode TRAVEL_MODE_ROUTE = 12;

Let's rip them out for good:

• remove from travel mode
• remove in scripting env
• remove from json travel mode translation
• adapt testbot profile
• rip out testbot cucumber tests

[MoKob]

The problem here is that if we remove these travel modes, we would also change the API. An assignment, even though not used so far, of these modes would not be possible anymore.

Like so many small changes, we should target their removal for 6.0.