fix: drop error-message step and fix evaluator gherkin conventions

Remove 'error message should contain' step (new step def, adds friction).
Fix evaluator suite to use 'a fallback value' instead of 'a default value'.
Add missing 'Given an evaluator' to new evaluator scenarios.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

Author: toddbaert

evaluator/gherkin/evaluator-refs.feature

@@ -16,7 +16,8 @@ Feature: Evaluator evaluator refs
 
   @evaluator-refs @evaluator-refs-whitespace
   Scenario Outline: Evaluator $ref resolves regardless of whitespace around the colon
-    Given a String-flag with key "<key>" and a default value "fallback"
+    Given an evaluator
+    And a String-flag with key "<key>" and a fallback value "fallback"
     And a context containing a key "email", with type "String" and with value "<email>"
     When the flag was evaluated with details
     Then the resolved details value should be "<value>"
@@ -32,8 +33,8 @@ Feature: Evaluator evaluator refs
 
   @evaluator-refs @non-existent-evaluator-ref
   Scenario: Ref to nonexistent evaluator yields parse error
-    Given a String-flag with key "ref-to-nonexistent-evaluator-flag" and a default value "fallback"
+    Given an evaluator
+    And a String-flag with key "ref-to-nonexistent-evaluator-flag" and a fallback value "fallback"
     When the flag was evaluated with details
     Then the resolved details value should be "fallback"
     And the error-code should be "PARSE_ERROR"
-    And the error message should contain "nonexistent_evaluator"

gherkin/targeting.feature

@@ -42,7 +42,6 @@ Feature: Targeting rules
     When the flag was evaluated with details
     Then the resolved details value should be "fallback"
     And the error-code should be "PARSE_ERROR"
-    And the error message should contain "nonexistent_evaluator"
 
   # custom operators
   # @fractional-v1: legacy float-based bucketing (abs(hash) / i32::MAX * 100)