using flatbuffers-java:1.7.2 from maven repo, removing embedded sources

Author: greenrobot

objectbox-java/build.gradle

@@ -19,6 +19,7 @@ dependencies {
     compile fileTree(include: ['*.jar'], dir: 'libs')
     compile project(':objectbox-java-api')
     compile 'org.greenrobot:essentials:3.0.0-RC1'
+    compile 'com.google.flatbuffers:flatbuffers-java:1.7.2'
     compile 'com.google.code.findbugs:jsr305:3.0.2'
 }