Remove unused code in solver package.

[cmnbroad]

This code appears to be unused, and causes (minor) problems on newer versions of Java, so I propose we remove it.

[codecov]

Codecov Report

Merging #7922 (f991a91) into master (8341ae5) will decrease coverage by 0.002%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #7922       +/-   ##
===============================================
- Coverage     87.072%   87.070%   -0.002%     
+ Complexity     37002     36941       -61     
===============================================
  Files           2221      2215        -6     
  Lines         173927    173691      -236     
  Branches       18793     18778       -15     
===============================================
- Hits          151441    151232      -209     
+ Misses         15850     15831       -19     
+ Partials        6636      6628        -8     

Impacted Files	Coverage Δ
...nder/utils/runtime/StreamingProcessController.java	68.182% <0.000%> (+0.909%)	⬆️

[cmnbroad]

Thanks @samuelklee!

[samuelklee]

Just for the record, as referenced in Slack, I managed to track down the previous PR in which this code was saved from the chopping block: #4181 But our current reasons are certainly compelling enough---we'll pour one out for Mehrtash's beloved solvers!