satcheck minisat2: make all solver hardness processing conditional

[tautschnig]

There is no need to run process_clause when its output wouldn't even be
used.

• 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/
• 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).
• 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

Merging #5708 (1d48d27) into develop (a0dbf74) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #5708      +/-   ##
===========================================
- Coverage    69.50%   69.50%   -0.01%     
===========================================
  Files         1243     1243              
  Lines       100690   100689       -1     
===========================================
- Hits         69989    69988       -1     
  Misses       30701    30701              

Flag	Coverage Δ
cproversmt2	43.11% <14.28%> (-0.04%)	⬇️
regression	66.40% <100.00%> (-0.01%)	⬇️
unit	32.22% <14.28%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/solvers/sat/cnf.h	77.77% <ø> (ø)
src/solvers/sat/cnf.cpp	83.25% <100.00%> (ø)
src/solvers/sat/satcheck_minisat2.cpp	70.58% <100.00%> (-0.25%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update a0dbf74...1d48d27. Read the comment docs.

[NlightNFotis]

LGTM