aes/x86/x86_64: Only use AES-NI when SSSE3 is available.

[briansmith]

Simplify feature detection logic. We don't have an easy way to test AES-NI without SSSE3, and it's not worth trying to hack something up.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.64%. Comparing base (6e04750) to head (bc307f6).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2359   +/-   ##
=======================================
  Coverage   96.64%   96.64%           
=======================================
  Files         176      176           
  Lines       21611    21611           
  Branches      526      526           
=======================================
+ Hits        20886    20887    +1     
  Misses        613      613           
+ Partials      112      111    -1     

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