Remove redundant charset validation test

The "charset validation UTF-8 multibyte sequence validation" test was duplicating
functionality already covered by existing tests:
- "charset validation ASCII range tests" already tests é, €, 🍕 multibyte sequences
- "charset validation edge cases" already covers invalid UTF-8 sequence rejection

This cleanup reduces test redundancy while maintaining full coverage of the
formatInvalidByteForError fix for proper UTF-8 validation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

enginetest/queries/script_queries.go

@@ -7228,39 +7228,6 @@ where
 			},
 		},
 	},
-	{
-		Name: "charset validation UTF-8 multibyte sequence validation",
-		SetUpScript: []string{
-			"create table utf8_validation_test (c char(10), v varchar(20), t text) character set utf8mb4;",
-		},
-		Assertions: []ScriptTestAssertion{
-			{
-				Query:    "set sql_mode = 'STRICT_TRANS_TABLES';",
-				Expected: []sql.Row{{types.OkResult{RowsAffected: 0}}},
-			},
-			// Test that valid multibyte sequences > 127 are accepted (fixes the b > asciiMax bug)
-			{
-				Query:    "insert into utf8_validation_test(c, v, t) values (UNHEX('C3A9'), UNHEX('E282AC'), UNHEX('F09F8D95'));", // é, €, 🍕 - valid UTF-8 sequences with bytes > 127
-				Expected: []sql.Row{{types.OkResult{RowsAffected: 1}}},
-			},
-			// Test that actual invalid UTF-8 sequences are still rejected
-			{
-				Query:          "insert into utf8_validation_test(c) values (UNHEX('C0C1'));", // Invalid overlong sequence
-				ExpectedErrStr: "Incorrect string value: '\\xC0\\xC1' for column 'c' at row 1",
-			},
-			{
-				Query:          "insert into utf8_validation_test(v) values (UNHEX('FE'));", // Invalid UTF-8 byte
-				ExpectedErrStr: "Incorrect string value: '\\xFE' for column 'v' at row 1",
-			},
-			// Verify the valid multibyte data was stored correctly
-			{
-				Query: "select HEX(c), HEX(v), HEX(t) from utf8_validation_test where c is not null and v is not null and t is not null;",
-				Expected: []sql.Row{
-					{"C3A9", "E282AC", "F09F8D95"}, // é, €, 🍕
-				},
-			},
-		},
-	},
 	{
 		Name: "charset validation issue #8893 - customer scenario",
 		SetUpScript: []string{