Revert "Add GUC backtrace_on_internal_error"
This reverts commit
a740b213d4b4d3360ad0cac696e47e5ec0eb8864.
Subsequent discussion showed that there was interest in a more general
facility to configure when server log events would produce backtraces,
and this existing limited way couldn't be extended in a compatible
way. So the consensus was to revert this for PostgreSQL 17 and
reconsider this topic for PostgreSQL 18.
Discussion: https://www.postgresql.org/message-id/flat/CAGECzQTChkvn5Xj772LB3%3Dxo2x_LcaO5O0HQvXqobm1xVp6%2B4w%40mail.gmail.com#
764bcdbb73e162787e1ad984935e51e3