Drop pure bionic build

travis/linux.bionic.before_install

@@ -1 +0,0 @@
-linux.stretch.before_install

travis/linux.bionic.install

@@ -1,11 +0,0 @@
-#!/bin/sh
-sudo apt-get install -y \
-	android-sdk \
-	android-sdk-platform-23 \
-	apksigner \
-	default-jdk-headless \
-	gettext \
-	gradle \
-	libgradle-android-plugin-java \
-	libicu4j-java \
-	libjaxb-api-java

travis/linux.bionic.script

@@ -1 +0,0 @@
-support/script

travis/support.bionic/build.gradle

@@ -1,20 +0,0 @@
-buildscript {
-    repositories {
-        maven { url "file:///usr/share/maven-repo" }
-    }
-
-    dependencies {
-        classpath "com.android.tools.build:gradle:debian"
-    }
-}
-
-apply plugin: "com.android.application"
-
-android {
-    compileSdkVersion 23
-    buildToolsVersion "27.0.1"
-}
-
-dependencies {
-    compile files("libs/android-support-v4.jar")
-}