[FIR JS] KT-57601: Get rid of the builtin provider

In this example we get 2 variants of `kotlin/toString()`:
one coming from the KLib provider, and the
other coming from the builtins provider.
These are identical deserialized functions.

^KT-57601 Fixed

compiler/build.gradle.kts

@@ -56,6 +56,7 @@ projectTest(
     defineJDKEnvVariables = listOf(JdkMajorVersion.JDK_1_8, JdkMajorVersion.JDK_11_0, JdkMajorVersion.JDK_17_0)
 ) {
     dependsOn(":dist")
+    useJsIrBoxTests(version = version, buildDir = "$buildDir/")
 
     workingDir = rootDir
     systemProperty("kotlin.test.script.classpath", testSourceSet.output.classesDirs.joinToString(File.pathSeparator))