Use EM_JS instead of EM_ASM in other.test_js_optimizer_parse_error [NFC] (#19702)

EM_ASM ends up with an index which is the address of a string constant,
which depends on other string constants in the program, for which reason
it did not just pass in WasmFS. I realized the simple solution is to just use
EM_JS there: that emits a nice simple JS function in which the parse error
we look for occurs.

Author: kripken

test/test_other.py

@@ -9074,19 +9074,16 @@ def test_js_optimizer_parse_error(self):
     # check we show a proper understandable error for JS parse problems
     create_file('src.c', r'''
 #include <emscripten.h>
+EM_JS(void, js, (void), {
+  var x = !<->5.; // wtf... this will error on the '<'
+});
 int main() {
-  EM_ASM({
-    var x = !<->5.; // wtf
-  });
+  js();
 }
 ''')
     stderr = self.expect_fail([EMCC, 'src.c', '-O2'] + self.get_emcc_args())
-    # TODO: To make this test work in WasmFS, the constant below must be
-    #       modified. It is the address in memory of the string constant of the
-    #       EM_ASM, and WasmFS has its own string constants that cause a
-    #       difference.
     self.assertContained(('''
-  1024: () => { var x = !<->5.; }
+function js() { var x = !<->5.; }
                          ^
 '''), stderr)