Remove the Travis configuration

Travis isn't being used. I found this confusing as I was going to re-enable unit tests, but then realized CircleCI is used instead.

.travis.yml

-#.travis.yml
-
-language: android
-jdk: oraclejdk8
-sudo: required
-
-android:
-  components: # Cookbooks version: https://github.com/travis-ci/travis-cookbooks/tree/9c6cd11
-    - tools # Update preinstalled tools from revision 24.0.2 to 24.4.1
-    - build-tools-25.0.3 # Match build-tools version used in build.gradle
-    - platform-tools # Update platform-tools to revision 25.0.3+
-    - tools # Update tools from revision 24.4.1 to 25.2.5
-    
-env:
-  global:
-    - API=26 # Android API level 26 by default
-    - TAG=google_apis # Google APIs by default, alternatively use default
-    - ABI=armeabi-v7a # ARM ABI v7a by default
-    - QEMU_AUDIO_DRV=none # Disable emulator audio to avoid warning
-    - ANDROID_HOME=/usr/local/android-sdk # Depends on the cookbooks version used in the VM
-    - TOOLS=${ANDROID_HOME}/tools # PATH order matters, exists more than one emulator script
-    - PATH=${ANDROID_HOME}:${ANDROID_HOME}/emulator:${TOOLS}:${TOOLS}/bin:${ANDROID_HOME}/platform-tools:${PATH}
-    - ADB_INSTALL_TIMEOUT=20 # minutes (2 minutes by default)
-
-install:
-  # List and delete unnecessary components to free space
-  - sdkmanager --list || true
-  - sdkmanager --uninstall "system-images;android-15;default;armeabi-v7a"
-
-  # Update sdk tools to latest version and install/update components
-  - echo yes | sdkmanager "tools"
-  - echo yes | sdkmanager "platforms;android-26" # Latest platform required by SDK tools
-  - echo yes | sdkmanager "platforms;android-${API}" # Android platform required by emulator
-  - echo yes | sdkmanager "extras;android;m2repository"
-  - echo yes | sdkmanager "extras;google;m2repository"
-  - echo yes | sdkmanager "extras;m2repository;com;android;support;constraint;constraint-layout;1.0.2"
-  - echo yes | sdkmanager "extras;m2repository;com;android;support;constraint;constraint-layout-solver;1.0.2"
-# - echo yes | sdkmanager "$EMULATOR" # Install emulator system image
-#   Create and start emulator
-# - echo no | avdmanager create avd -n acib -k "$EMULATOR" -f --abi "$ABI" --tag "$TAG"
-# - emulator -avd acib -engine classic -no-window -verbose -qemu -m 512 &
-
-before_script:
-# - echo y | android update sdk --no-ui --all --filter tools,platform-tools
-# - echo y | android update sdk --no-ui --all --filter android-25
-# - echo y | android update sdk --no-ui --all --filter extra-android-m2repository,extra-android-support
-# - echo y | android update sdk --no-ui --all --filter extra-google-m2repository,extra-google-google_play_services
-# - echo y | android update sdk --no-ui --all --filter build-tools-25.0.3
-# - echo yes | sdkmanager "extras;m2repository;com;android;support;constraint;constraint-layout;1.0.2"
-# - echo yes | sdkmanager "extras;m2repository;com;android;support;constraint;constraint-layout-solver;1.0.2"
- - ./gradlew dependencies
-
-script:
- - ./gradlew checkstyle findbugs pmd