RevertBiography: fixed off-by-1 in iwd2 case

and nobody can start as a multiclass
pst: removed a column from bios.2da

useless and would look odd once the rest are converted
iwd2: removed a useless column
bg1: removed a useless column from bios.2da

still unused, but not for long
bg1: fixed cleric/priest mix up in bios.2da
GetProtagonistBiography: use bios.2da instead of hardcoding strrefs

also opens the way for potential reuse in pst and iwd2
(what's up with bg2??)