Fix DocString Warning

[dhendryc]

The issue was that the abstract function is_linear_feasible existed twice with different explanations.

One was for the BoundedLinearMinimizationOracle, the other for SimpleBoundedLMO. By that the two do sightly different things, as the is_linear_feasibleof the SimpleBoundedLMO is a subroutine of is_linear_feasible function for the ManagedBoundedLMO.

Renamed it to is_simple_linear_feasible.

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (ee5cc6c) 86.23% compared to head (3b51b7d) 86.36%.
Report is 7 commits behind head on main.

Files	Patch %	Lines
src/interface.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #169      +/-   ##
==========================================
+ Coverage   86.23%   86.36%   +0.13%     
==========================================
  Files          17       17              
  Lines        1482     1482              
==========================================
+ Hits         1278     1280       +2     
+ Misses        204      202       -2     

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