Remove <uses-sdk /> from manifest.

The Android Gradle plugin prefers to retrieve this value from build.gradle, and some versions of the plugin actively complain about the tag being there.

Closes #1435

dependencies/extension-api/src/main/AndroidManifest.xml

@@ -1,6 +1,4 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="org.haxe.extension" >
     
-    <uses-sdk android:minSdkVersion="::ANDROID_MINIMUM_SDK_VERSION::" android:targetSdkVersion="::ANDROID_TARGET_SDK_VERSION::" />
-    
 </manifest>