Fix build error: Remove duplicate QueryErrorTest type definition

- Use existing QueryErrorTest struct from queries package
- Remove custom type redeclaration that caused build failures
- Verified charset validation tests work against MySQL comparison server

Author: elianddb

enginetest/queries/charset_validation_queries.go

@@ -46,12 +46,6 @@ var CharsetValidationErrorTests = []QueryErrorTest{
 	},
 }
 
-// QueryErrorTest represents a test case that expects an error
-type QueryErrorTest struct {
-	Query          string
-	ExpectedErrStr string
-}
-
 // CharsetValidationScriptTest represents comprehensive charset validation scenarios  
 var CharsetValidationScriptTest = ScriptTest{
 	Name: "Charset validation behavior for issue #8893",