Remove old Fort Mode from frontend
Part of ripping out Fort Mode from game schemes. This time for real.
- Remove the game modifier button "Fort Mode"
- Remove the scheme "Fort Mode"
- Remove some fort mode handling code
- Keep gfForts symbol to not mess up things too much
- Old schemes are still supported, the fortsmode parameter is just ignored
[patterns]
**.h = native
**.c = native
**.cpp = native
**.lua = native
**.txt = native
**.pas = native
**.inc = native
**.hs = native