Remove warning about the WAL format being unstable

[jeltz]

In the next release the WAL will no longer be in beta testing.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.19%. Comparing base (da899e0) to head (e0560d8).
⚠️ Report is 5 commits behind head on TDE_REL_17_STABLE.

❌ Your project status has failed because the head coverage (82.19%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@                  Coverage Diff                  @@
##           TDE_REL_17_STABLE     #515      +/-   ##
=====================================================
- Coverage              82.22%   82.19%   -0.03%     
=====================================================
  Files                     25       25              
  Lines                   3179     3174       -5     
  Branches                 515      515              
=====================================================
- Hits                    2614     2609       -5     
  Misses                   456      456              
  Partials                 109      109              

Components	Coverage Δ
access	83.47% <ø> (-0.10%)	⬇️
catalog	87.60% <ø> (-0.02%)	⬇️
common	77.77% <ø> (ø)
encryption	72.97% <ø> (ø)
keyring	73.21% <ø> (ø)
src	94.15% <ø> (ø)
smgr	95.29% <ø> (ø)
transam	∅ <ø> (∅)

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[AndersAstrand]

s/WAL/WAL encryption/

[jeltz]

Fixed.