chore: Revert removing feature toggle for fetchmail debug

target/bin/debug-fetchmail

@@ -5,7 +5,13 @@ source /usr/local/bin/helpers/log.sh
 # shellcheck source=../scripts/startup/setup.d/fetchmail.sh
 source /usr/local/bin/setup.d/fetchmail.sh
 
-_setup_fetchmail
+# TODO: This should probably not implicitly enable the feature.
+# The setup method will feature gate and output a debug log if
+# the feature is not enabled.
+#
+# Dropping the ENV here will require updating legacy test:
+# test/tests/parallel/set3/scripts/setup_cli.bats
+ENABLE_FETCHMAIL=1 _setup_fetchmail
 
 su -s /bin/sh -c "/usr/bin/fetchmail \
   --verbose \