Fix validation for Action.Type field

The now removed error handling was used prior to refactoring
applied in commit 7ef6d52.

credit: Thanks to @ArcticXWolf for reporting this.

- refs GH-268
- refs GH-251

adaptivecard/adaptivecard.go

@@ -1934,12 +1934,6 @@ func (a Action) Validate() error {
  // Optional, but only supported by the Action.ShowCard type.
  case a.Card != nil:
  v.FieldHasSpecificValue(a.Type, "type", TypeActionShowCard, "type", ErrInvalidType)
-
- return fmt.Errorf(
- "error: specifying a Card is unsupported for Action type %q: %w",
- a.Type,
- ErrInvalidFieldValue,
- )
  }
 
  // Return the last recorded validation error, or nil if no validation