mynewt: remove version.yml and references

With the merge of https://github.com/apache/mynewt-newt/pull/365 `newt`
does not use `version.yml` files anymore, so remove the file and
references to updating it in the release process.

Testing a MCUBoot release now depends on `newt` `master` or `> 1.7.0`
(to be released).

Signed-off-by: Fabio Utzig <utzig@apache.org>
diff --git a/docs/release.md b/docs/release.md
index 328531c..34bd5c3 100644
--- a/docs/release.md
+++ b/docs/release.md
@@ -51,8 +51,7 @@
 the rc step is finished, the release needs to be exported by modifying
 `repository.yml` in the root directory; it must be updated with the
 new release version, including updates to the pseudo keys
-(`*-(latest|dev)`). Similarly `version.yml` must have its `repo.version`
-key updated with the version number being released.
+(`*-(latest|dev)`).
 
 ## Tagging and Release
 
@@ -82,10 +81,4 @@
 git push origin va.b.c-rcn
 ```
 
-## Update Mynewt version.yml
-
-On master `version.yml` must always have its `repo.version`
-key set to "0.0.0" to this must be done now that the release
-is finished.
-
 [semver]: http://semver.org/