Removing loop_var in device.py

[GraysonBellamy]

🚀 Feature Request

loop_var variable seems to mirror the numbers in the "_Setpt" variables in "statistics". See if we can remove it to reduce variables and use existing dictionary instead.

🔈 Motivation

Reduces number of variables and eliminates duplication.

🛰 Alternatives

It may be required but is not clear to me.

📎 Additional context

[GraysonBellamy]

Updated "loop_control_alg" and "loop_control_var" functions to refer to 'statistics' list instead of 'loop_vars', then removed 'loop_vars'. Tested both to verify.