Add dependencies on org.apache.http.legacy where needed

Incorporates two main changes:
* Stops statically including the org.apache.http.legacy library. That library is
  a stubs library so it makes no sense to statically include it.
* Adds uses-library declaration for org.apache.http.legacy to those packages
  that depend on org.apache.http.legacy, either directly or transitively.

The following change descriptions were generated automatically and so
may be a little repetitive. They are provided to give the reviewer
enough information to check the comments match what has actually been
changed and check the reasoning behind the changes.

* libwvdrmengine/test/castv2/AndroidManifest.xml
    Added <uses-library> for org.apache.http.legacy to ensure classes
    are provided at runtime. It is marked as optional as the
    application is intended to be run on versions that do not provide
    the library, but provide the classes by default, i.e. its
    minSdkVersion is < M (23).

* libwvdrmengine/test/java/AndroidManifest.xml
    Added <uses-library> for org.apache.http.legacy to ensure classes
    are provided at runtime. It is marked as optional as the
    application is intended to be run on versions that do not provide
    the library, but provide the classes by default, i.e. its
    minSdkVersion is < M (23).

Bug: 18027885
Test: m -j32 droid && adb reboot bootloader && fastboot flashall -w
Change-Id: I4eb4621bc4c2f481c0d909acac871187f006e145

libwvdrmengine/test/castv2/AndroidManifest.xml

@@ -11,6 +11,7 @@
     <application android:icon="@drawable/icon" android:label="@string/app_name" android:theme="@android:style/Theme.Holo.NoActionBar">
       <uses-library android:name="com.android.mediadrm.signer"
                 android:required="true" />
+      <uses-library android:name="org.apache.http.legacy" android:required="false" />
       <activity android:name="CastSignAPITest"
                 android:label="@string/app_name"
                 android:screenOrientation="landscape">