[android] Remove autogenerated file from tree

developer-config.xml gets generated on build time with the token
set for the env var MAPBOX_ACCESS_TOKEN. Because the file was checked to
the git repo, it was not being regenerated and thus, crashing the
test app accusing no token set.

android/MapboxGLAndroidSDKTestApp/src/main/res/values/developer-config.xml

@@ -1,4 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<resources>
-    <string name="access_token">null</string>
-</resources>