RULEAPI-788 Turn diff-view validation on (#2883)

ci/asciidoc_validation/validate.sh

@@ -80,10 +80,7 @@ bad_diffs=$(grep_nofail -e 'DIFF' "${TMPOUT_DIR}/asciidoc_introspection" | extra
 if [[ -n "$bad_diffs" ]]
 then
   printf >&2 'ERROR: Diff highlighting is used incorrectly:\n-----\n%s\n-----\n' "$bad_diffs"
-  if [[ -n "${RUNNING_CI_INTEGRATION_TEST:-}" ]]
-  then
-    exit_code=1 # FIXME: there are currently validation errors in the repo. Unconditionally enable this line when they are all fixed.
-  fi
+  exit_code=1
 fi
 
 exit $exit_code

ci_tests/asciidoc_validation/run_tests.sh

@@ -4,8 +4,6 @@
 
 set -uo pipefail
 
-export RUNNING_CI_INTEGRATION_TEST=1 # FIXME remove this once it's no longer needed in validate.sh
-
 # We could write complex checks to ensure only specific commands fail and emit
 # a specific error message. Instead, we rely on `set -xe` to consistently and
 # reliably exit with non-zero if any command fails and pinpoint which command