Remove useless "Am I really in a script" checks in `import.source` tests

[nicolo-ribaudo]

See #4374 (comment)

[nicolo-ribaudo]

I did tentatively assign this to myself, but cc @legendecas in case you want to do it :)

[legendecas]

It was dated back to

test262/src/dynamic-import/eval-script-code-host-resolves-module-code.case

Lines 8 to 11 in 84f8202

	//- setup
	// This is still valid in script code, and should not be valid for module code
	// https://tc39.github.io/ecma262/#sec-scripts-static-semantics-lexicallydeclarednames
	var smoosh; function smoosh() {}

.