Delete alternative objective functions in allocation

[Jingru923]

What
In allocation, solving the optimization problem means finding out the best solution that narrowing the gap between the user demand and the allocated demand. In the optimization problem, there are four type of object functions, we would like to have only linear absolute

Why
We would like our code to be simpler and more maintainable. @visr had a discussion with Ailbhe and the conclusion is that we can just keep the linear absolute object functions.

How
Disable the option for object function. Delete all the relevant part of the other 3 object function.

[visr]

Reopening since #1193 only disabled other options, we still need to delete the code and possibly refactor a bit to simplify code now that we don't support multiple choices.