[Remoting Android] Change target SDK version to 28

This CL bumps the targetSdkVersion to 28 since our app should be fully
supporting Pie features (i.e. cutout adjustments).

Bug: 831670
Change-Id: I7e1507f4c3c56ed802de3af75eafea3b9024d826
Reviewed-on: https://chromium-review.googlesource.com/1188897
Reviewed-by: Joe Downing <joedow@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586031}

Author: ywh233

remoting/android/java/AndroidManifest.xml.jinja2

@@ -2,7 +2,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
         package="{{ APK_PACKAGE_NAME }}">
     <uses-sdk android:minSdkVersion="14"
-            android:targetSdkVersion="26"/>
+            android:targetSdkVersion="28"/>
     <uses-permission android:name="android.permission.INTERNET"/>
     <uses-feature android:glEsVersion="0x00020000" android:required="true" />