Remove GC during Highs_run

[odow]

It is not thread-safe to call Highs_destory during Highs_run: ERGO-Code/HiGHS#3136 (comment)

This was originally added by #178. The original motivation isn't needed anymore, because we have a default callback the re-enters Julia to handle interrupts etc.

This might still not fix the thread-safety issue; that might need some changes in HiGHS itself.

[odow]

So this is arguably just a thread-safety bug in HiGHS: ERGO-Code/HiGHS#3136 (comment)

Maybe we don't need any change here.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (5f3e3b7) to head (1285731).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #345   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            2         2           
  Lines         1600      1597    -3     
=========================================
- Hits          1600      1597    -3     

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[odow]

Closing because this was just a bug in HiGHS. The GC thing can still be useful because we don't call back into HiGHS for simplex.