Replaced all calls to `imm_draw_line` by plain `immVertex2f` calls, and removed `imm_draw_line`, as that function was not supposed to exist in the first place, and causes unnecessary calls to `immBegin`/`immEnd`. Part of T49043
Replaced all calls to `imm_draw_line` by plain `immVertex2f` calls, and removed `imm_draw_line`, as that function was not supposed to exist in the first place, and causes unnecessary calls to `immBegin`/`immEnd`. Part of T49043