Remove Constant Aggregate nodes from SVFIR

[mbarbar]

These do not appear to be used anywhere.

[mbarbar]

I'm not really sure if we want to keep this for future or anything, but I incline to think if we don't need it now, we don't need to have it now.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 65.82%. Comparing base (b086369) to head (c88147d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1872      +/-   ##
==========================================
+ Coverage   65.78%   65.82%   +0.03%     
==========================================
  Files         251      251              
  Lines       24699    24665      -34     
  Branches     4661     4660       -1     
==========================================
- Hits        16249    16235      -14     
+ Misses       8450     8430      -20     

Files with missing lines	Coverage Δ
svf-llvm/lib/SVFIRBuilder.cpp	89.12% <100.00%> (+0.21%)	⬆️
svf/include/SVFIR/SVFIR.h	92.77% <ø> (+1.37%)	⬆️
svf/include/SVFIR/SVFValue.h	88.88% <ø> (ø)
svf/include/SVFIR/SVFVariables.h	70.83% <ø> (+2.55%)	⬆️
svf/lib/SVFIR/SVFVariables.cpp	68.75% <ø> (+0.95%)	⬆️

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