Add the HEAL_LOCATION_NONE constant

[sphericalice]

Description

Adds the HEAL_LOCATION_NONE constant and renames some variables (warp implies something different to healLocation imo). Also uses the TRY_FREE_AND_SET_NULL macro for when sFlyMap is freed in CB_ExitFlyMap.

Discord contact info

Spherical Ice#4683

[GriffinRichards]

Looks good to me. Unfortunately this is going to cause issues with Porymap.

At the moment Porymap is responsible for writing include/constants/heal_locations.h, and it determines what constants should go in that file based on what's present in the table sHealLocations. HEAL_LOCATION_NONE isn't present in that table, and so the define will be removed and the user's repo won't build.

I'll mark it as a draft for now until (if ever) that's resolved on Porymap's end.