minor: drop main-kts tests on oldBE

it is not supported anymore

build.gradle.kts

@@ -666,7 +666,6 @@ tasks {
 //        dependsOn(":kotlin-scripting-jvm-host-test:embeddableTest")
         dependsOn(":kotlin-scripting-jsr223-test:embeddableTest")
         dependsOn(":kotlin-main-kts-test:test")
-        dependsOn(":kotlin-main-kts-test:testWithIr")
         dependsOn(":kotlin-scripting-ide-services-test:test")
         dependsOn(":kotlin-scripting-ide-services-test:embeddableTest")
     }

libraries/tools/kotlin-main-kts-test/build.gradle.kts

@@ -23,13 +23,6 @@ sourceSets {
 projectTest(parallel = true) {
     dependsOn(":dist")
     workingDir = rootDir
-    systemProperty("kotlin.script.base.compiler.arguments", "-Xuse-old-backend")
-}
-
-projectTest(taskName = "testWithIr", parallel = true) {
-    dependsOn(":dist")
-    workingDir = rootDir
-    systemProperty("kotlin.script.base.compiler.arguments", "-Xuse-ir")
 }
 
 projectTest(taskName = "testWithK2", parallel = true) {