THRIFT-5633: move xenial to old, deprecate xenial in travis build (#2690)

* move xenial to old, deprecate xenial in travis build

* add back stage of docker
diff --git a/lib/kotlin/settings.gradle.kts b/lib/kotlin/settings.gradle.kts
index 2eff402..c252add 100644
--- a/lib/kotlin/settings.gradle.kts
+++ b/lib/kotlin/settings.gradle.kts
@@ -19,14 +19,7 @@
 pluginManagement {
     plugins {
         kotlin("jvm") version "1.6.10"
-        // per https://github.com/cortinico/ktfmt-gradle/tags the latest version requires Gradle 7.4 which in turn
-        // requires Java 11, failing the xenial build which is still on Java 8. Here we both configure the plugin
-        // but with different version, and only enabling ktfmt configure for Java 11+, to make the legacy build happy
-        if (JavaVersion.current().isJava11Compatible) {
-            id("com.ncorti.ktfmt.gradle") version "0.8.0"
-        } else {
-            id("com.ncorti.ktfmt.gradle") version "0.5.0"
-        }
+        id("com.ncorti.ktfmt.gradle") version "0.8.0"
     }
 }