remove duplicate SATCHECK_* defines

[kroening]

The SATCHECK_* defines (e.g., SATCHECK_MINISAT2) are defined both in src/solvers/satcheck.h, and in config.inc.

This removes the instance in config.inc, in an effort to de-clutter the compiler command line. Users of the macros can include the header file.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• n/a Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.76%. Comparing base (83f61a4) to head (fd53c32).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8501   +/-   ##
========================================
  Coverage    78.76%   78.76%           
========================================
  Files         1728     1728           
  Lines       198925   198925           
  Branches     18326    18295   -31     
========================================
  Hits        156686   156686           
  Misses       42239    42239           

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