VOL-1941: Use protobufs from the voltha-protos repo, not a copy

- Use protobufs from the voltha-protos repo, not a copy
- Provided option to specify the openolt proto version via make option
- Removed duplicate README.md

Change-Id: Id67714c8119521f8358aaa9245268c47b7e843cf
diff --git a/.gitignore b/.gitignore
index da69683..6bf2e45 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,5 +28,8 @@
 # Test report
 **/test_openolt_report.xml
 
+# Downloaded voltha-protos file
+voltha_protos
+
 # IntelliJ Files
 .idea