[PG-1695] Remove extra word in error message for existing key

[AndersAstrand]

This "to" had no business being in this message.

This should be fixed before release, so this PR is for the release branch.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.68%. Comparing base (5610639) to head (4ef42c9).
Report is 4 commits behind head on release-17.5.2.

❌ Your project status has failed because the head coverage (84.68%) 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                 @@
##           release-17.5.2     #449      +/-   ##
==================================================
+ Coverage           84.66%   84.68%   +0.02%     
==================================================
  Files                  21       21              
  Lines                2589     2593       +4     
  Branches              402      401       -1     
==================================================
+ Hits                 2192     2196       +4     
  Misses                316      316              
  Partials               81       81              

Components	Coverage Δ
access	81.11% <ø> (ø)
catalog	88.22% <ø> (ø)
common	77.77% <ø> (ø)
encryption	73.45% <ø> (ø)
keyring	72.88% <ø> (ø)
src	91.54% <ø> (+0.09%)	⬆️
smgr	94.85% <ø> (-0.03%)	⬇️
transam	∅ <ø> (∅)

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