Remove non-Array support for idl_test arguments srcs and deps (#27420)

diff --git a/resources/idlharness.js b/resources/idlharness.js
index 5a97b27..76131e7 100644
--- a/resources/idlharness.js
+++ b/resources/idlharness.js
@@ -3543,8 +3543,6 @@
 function idl_test(srcs, deps, idl_setup_func) {
     return promise_test(function (t) {
         var idl_array = new IdlArray();
-        srcs = (srcs instanceof Array) ? srcs : [srcs] || [];
-        deps = (deps instanceof Array) ? deps : [deps] || [];
         var setup_error = null;
         const validationIgnored = [
             "constructor-member",