Fix libhs builds v2

[liwilson1]

Unset ac_cv_header_hs_h before checking for header. This allows hyperscan to be included in compilation when switching from a non-hs build to a hs build.

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• I have read the contributing guide lines at
  https://docs.suricata.io/en/latest/devguide/contributing/contribution-process.html

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• I have signed the Open Information Security Foundation contribution agreement at
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Changes (if applicable):

• I have updated the User Guide (in doc/userguide/) to reflect the changes made
• I have updated the JSON schema (in etc/schema.json) to reflect all logging changes
  (including schema descriptions)
• I have created a ticket at
  https://redmine.openinfosecfoundation.org/projects/suricata/issues

Link to ticket: https://redmine.openinfosecfoundation.org/issues/

Describe changes:

• Unset ac_cv_header_hs_h variable before checking for header. This prevents an issue we are seeing when switching from a non-hs build to a hs build. The cached 'no' value (from the non-hs build) is used by AC_CHECK_HEADER, resulting in hyperscan not being compiled into Suricata.

Updates commit message from #11836

[github-actions]

NOTE: This PR may contain new authors.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.54%. Comparing base (45eb7e4) to head (51174d4).
Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11841      +/-   ##
==========================================
- Coverage   82.60%   82.54%   -0.06%     
==========================================
  Files         912      912              
  Lines      249351   249351              
==========================================
- Hits       205965   205829     -136     
- Misses      43386    43522     +136     

Flag	Coverage Δ
fuzzcorpus	60.42% <ø> (-0.18%)	⬇️
livemode	18.76% <ø> (+0.03%)	⬆️
pcap	44.08% <ø> (+0.02%)	⬆️
suricata-verify	61.99% <ø> (-0.05%)	⬇️
unittests	58.94% <ø> (+<0.01%)	⬆️

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[victorjulien]

Merged in #11858, thanks!