doc: API lifecycle: Require creating a issue to track removal

As discussed in the TSC meeting of 2019/03/27:
To ensure that we do not forget to remove an API 2 releases later
and to provide a bit better visibility about when the removal
is planned, require that a GH issue be created, and that this
issue be added to the roadmap for the apropriate release.

As a free bonus:
Removed a redundant line in the list and added one missing article.

Signed-off-by: Alberto Escolar Piedras <alpi@oticon.com>

doc/development_process/api_lifecycle.rst

@@ -100,10 +100,12 @@ The following are the requirements for deprecating an existing API:
 
   - Mark as deprecated
   - Document the deprecation
-  - All usage in Zephyr for deprecated API needs to be modified
-  - Change needs to be atomic and bisectable
   - Code using the deprecated API needs to be modified to remove usage of said
     API
+  - The change needs to be atomic and bisectable
+  - Create a GitHub issue to track the removal of the deprecated API, and
+    add it to the roadmap targeting the appropriate release
+    (in the example above, 1.16).
 
 During the deprecation waiting period, the API will be in the ``deprecated``
 state. The Zephyr maintainers will track usage of deprecated APIs on
@@ -130,5 +132,6 @@ the corresponding documentation, and communicate the removal in the usual ways:
 the release notes, mailing lists, Github issues and pull-requests.
 
 If it's not OK to remove the API, the maintainers will continue to support
-migration and aim to remove the API in the next release.
+migration and update the roadmap with the aim to remove the API in the next
+release.