Build: remove explicit enabling of RangeUntilOperator

This feature is enabled by default since 1.8. Using the `-XXLanguage`
compiler argument leads to big warnings which are distracting during the
build.

libraries/stdlib/js-ir/build.gradle.kts

@@ -146,7 +146,6 @@ tasks.withType<KotlinCompile<*>>().configureEach {
         "-opt-in=kotlin.ExperimentalUnsignedTypes",
         "-opt-in=kotlin.ExperimentalStdlibApi",
         "-opt-in=kotlin.io.encoding.ExperimentalEncodingApi",
-        "-XXLanguage:+RangeUntilOperator",
     )
 }