Remove unused inventory_position

[AMurkin]

Summary

SUMMARY: None

Purpose of change

Fix

src/player.cpp: In member function ‘void player::use(item_location)’:
src/player.cpp:5224:9: error: unused variable ‘inventory_position’ [-Werror=unused-variable]
     int inventory_position = loc.where() == item_location::type::character ?
         ^~~~~~~~~~~~~~~~~~
cc1plus: all warnings being treated as errors

Describe the solution

Delete two LOC.
It compiles.