Remove vendored copy of fbjni (#530)

Summary:
Pull Request resolved: https://github.com/facebook/flipper/pull/530

Use the pre-release of fbjni instead of our bundled copy. I hope this can be made a little less awkward, but it works for now.

Reviewed By: jknoxville

Differential Revision: D16988077

fbshipit-source-id: 936e414f9b2bf82ccb54b107228d79d01acdbf14

build.gradle

@@ -31,6 +31,11 @@ subprojects {
         mavenCentral()
         jcenter()
 
+        maven {
+            // TODO: Remove once this is on official JCenter.
+            url 'https://dl.bintray.com/facebook/maven/'
+        }
+
         if (isSnapshot()) {
             maven { url 'https://oss.sonatype.org/content/repositories/snapshots/' }
         }