Add config combination file for auto config generator to watch (#294)

* Add config combination file for auto config generator to watch

Deleting old JSON database of published toolchain configs which is not
expected to be used any more.

* Address comments

* Rename dir

configs/dependency-tracking/README.md

diff --git a/configs/dependency-tracking/README.md b/configs/dependency-tracking/README.md
new file mode 100644
index 0000000..7ca0d17
--- /dev/null
+++ b/configs/dependency-tracking/README.md
@@ -0,0 +1,21 @@
+This directory contains YAML files which are used to track dependencies for 
+configs generated for specific RBE toolchain containers.
+
+A single dependency tracking file indicates the latest bazel version and 
+toolchain container the corresponding toolchain configs were last generated for. 
+When a new bazel versions or toolchain container version is available, the 
+dependency tracking file will be automatically updated by the config dependency 
+update service. This in turn will trigger a GCB build to generate the new 
+configs.
+
+The following is an example YAML config for the RBE Ubuntu 16.04 container.
+```yaml
+# Latest bazel version configs were generated for.
+bazel: "0.21.0"
+
+# Config version
+version: "7.0.0-r342117"
+```
+
+Note: Comments in the YAML configs will not be preserved by the dependency
+update service.

configs/dependency-tracking/ubuntu16_04.yaml

diff --git a/configs/dependency-tracking/ubuntu16_04.yaml b/configs/dependency-tracking/ubuntu16_04.yaml
new file mode 100644
index 0000000..c09f7ed
--- /dev/null
+++ b/configs/dependency-tracking/ubuntu16_04.yaml
@@ -0,0 +1,3 @@
+bazel: "0.21.0"
+version: "7.0.0-r342117"
+

configs/published_toolchain_configs.json

diff --git a/configs/published_toolchain_configs.json b/configs/published_toolchain_configs.json
deleted file mode 100644
index 7dd4387..0000000
--- a/configs/published_toolchain_configs.json
+++ /dev/null
@@ -1,2 +0,0 @@
-[]
-