No issue: ignore ExpiredTargetSdkVersion lint rule

[severinrudie]

Pull Request checklist

• [ ] This PR includes thorough tests or an explanation of why it does not
• [ ] This PR includes a CHANGELOG entry or does not need one
• [ ] The UI tests are passing after this PR (./gradlew connectedAmazonWebViewDebugAndroidTest)
• [ ] I have considered adding QA labels on the associated issue (not this PR; qa-ready or qa-denied)

[mcomella]

Android Lint failed with:

  The first 3 errors (out of 7) were:
  /home/travis/build/mozilla-mobile/firefox-echo-show/app/src/debug/AndroidManifest.xml:5: Error: Expecting an activity to have android.intent.category.LEANBACK_LAUNCHER intent filter. [MissingLeanbackLauncher]
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   ~~~~~~~~
  /home/travis/build/mozilla-mobile/firefox-echo-show/app/src/main/AndroidManifest.xml:5: Error: Expecting an activity to have android.intent.category.LEANBACK_LAUNCHER intent filter. [MissingLeanbackLauncher]
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   ~~~~~~~~
  /home/travis/build/mozilla-mobile/firefox-echo-show/app/src/debug/AndroidManifest.xml:5: Error: Hardware feature android.hardware.touchscreen not explicitly marked as optional  [ImpliedTouchscreenHardware]
  <manifest xmlns:android="http://schemas.android.com/apk/res/android"
   ~~~~~~~~

[mcomella]

Removing review request: Android lint still failed so I think it'd make more sense to review this when it's all fixed up.

@Baron-Severin FYI

[dnarcese]

Fixed in #302