Remove the GUC mention in the error message as this config is meant for advanced users

[tejeswarm]

DESCRIPTION: Remove the GUC, citus.enable_unsafe_triggers, mention in the error message as this config is meant for advanced users.

[codecov[bot]]

Codecov Report

Merging #6159 (4a4ef2d) into main (31cdf27) will decrease coverage by 0.00%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #6159      +/-   ##
==========================================
- Coverage   92.90%   92.89%   -0.01%     
==========================================
  Files         252      252              
  Lines       52940    52940              
==========================================
- Hits        49183    49179       -4     
- Misses       3757     3761       +4