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>