Revert [JS IR] commits that failed build

Revert "[JS IR] Build hybrid versions of stdlib and kotlin.test"
This reverts commit b9f88350dd.

Revert "[JS IR] Add gradle plugin integration tests"
This reverts commit d872b27663.

Revert "Update bootstrap"
This reverts commit bc47594c7a.

Revert "[JS IR] Support generating both IR and pre-IR libraries"
This reverts commit 1b8df45bfe.

libraries/kotlin.test/js/build.gradle

@@ -16,11 +16,7 @@ dependencies {
 }
 
 compileKotlin2Js {
-    kotlinOptions.freeCompilerArgs = [
-            "-Xallow-kotlin-package",
-            "-Xuse-experimental=kotlin.contracts.ExperimentalContracts",
-            "-Xir-produce-klib-dir"
-    ]
+    kotlinOptions.freeCompilerArgs = ["-Xallow-kotlin-package", "-Xuse-experimental=kotlin.contracts.ExperimentalContracts"]
     kotlinOptions {
         moduleKind = "umd"
         outputFile = "${buildDir}/classes/main/kotlin-test.js"