Mark PermissionDelegation as unsupported, for 2.6.1-rc2

[Bronek]

High Level Overview of Change

PermissionDelegation amendment requires more work, so we mark it as "unsupported" for now.

This release candidate is merging to the release branch.

This PR must be merged manually using a push. Do not use the Github UI.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.8%. Comparing base (8d01f35) to head (c46888f).
⚠️ Report is 2 commits behind head on release.

Additional details and impacted files

@@           Coverage Diff           @@
##           release   #5805   +/-   ##
=======================================
  Coverage     78.8%   78.8%           
=======================================
  Files          814     814           
  Lines        71310   71310           
  Branches      8345    8346    +1     
=======================================
+ Hits         56192   56197    +5     
+ Misses       15118   15113    -5     

Files with missing lines	Coverage Δ
src/libxrpl/protocol/BuildInfo.cpp	98.2% <ø> (ø)

... and 3 files with indirect coverage changes

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