test(linter/prefer-namespace-keyword): remove test case with invalid syntax (#15833)

Author: camc314

crates/oxc_linter/src/rules/typescript/prefer_namespace_keyword.rs

@@ -100,7 +100,6 @@ fn test() {
             module foo {}
         }
         ",
-        "module foo.'a'",
     ];
 
     let fix = vec![

crates/oxc_linter/src/snapshots/typescript_prefer_namespace_keyword.snap

@@ -49,9 +49,3 @@ source: crates/oxc_linter/src/tester.rs
  4 │         }
    ╰────
   help: Replace `module` with `namespace`.
-
-  × Unexpected token
-   ╭─[prefer_namespace_keyword.tsx:1:12]
- 1 │ module foo.'a'
-   ·            ───
-   ╰────