Remove unused harness file

The harness file `Test262Error.js` has not contained executable code since it
was introduced in this project [1]. The definition of the `Test262Error`
function has consistently been located in the `sta.js` harness file which test
runners are expected to inject into the test environment.

Remove the file and all references to it.

[1] See commit c33bf0e0

test/language/statements/while/S12.6.2_A9.js

@@ -5,7 +5,6 @@
 info: "\"while\" Statement is evaluated without syntax checks"
 es5id: 12.6.2_A9
 description: Throwing system exception inside "while" loop
-includes: [Test262Error.js]
 ---*/
 
 //////////////////////////////////////////////////////////////////////////////

test/language/types/reference/8.7.2-3-a-2gs.js

@@ -7,7 +7,6 @@ description: >
     Strict Mode - 'runtime' error is thrown before LeftHandSide
     evaluates to an unresolvable Reference
 flags: [onlyStrict]
-includes: [Test262Error.js]
 ---*/
 
 assert.throws(Test262Error, function() {