Remove CalcPlrStaff()

[kphoenix137]

This function is duplicate logic of the CalcPlrItemVals() logic for staves, which creates the potential for bugs.

CalcPlrInv():
CalcPlrItemVals() iterates each equipped item, and accumulates the spell from each item, then writes the bitmask to the Player struct variable that holds staff spells.

CalcPlrStaff is then called if player is myPlayer, and checks the left hand specifically with some conditions to see if it should add the spell from the staff to the Player struct variable. CalcPlrStaff() is also utilized to check if the player should continue having the staff spell after consuming a charge. This PR bypasses the need for that by directly calling CalcPlrInv() when consuming a charge, so we consistently call CalcPlrInv() any time there is an update in any form to the player's equipped items. This also keeps the logic in one place to avoid discrepancies.