runtime: Remove "features the runtime chooses to support"

[wking]

Step 3 of the lifecycle from before this commit had two sentences which both landed in #384. I pushed back a bit on the entry then, but we seem to be pretty comfortable with the current "keep all lifecyle entries in a one-layer enumerated list" approach, so I'm leaving that alone in this commit. Step 3 isn't really a lifecycle step though, it's more about clarifying that you can jump around in the lifecycle instead of hitting all the steps in consecutive order. In this commit, I've addressed that in a new paragraph that follows the list.

The other sentence from the old step 3 doesn't need replacing, because the limits are already covered in more detail in the operation sections themselves. For example, the 'delete' operation has:

Attempting to delete a container that does not exist MUST generate an error. Attempting to delete a container whose process is still running MUST generate an error.

I don't see the need to call generic attention to that idea, and especially do not think that an entry in the lifecycle list is the right place for such a generic call-out.

[wking]

Besides the removal of the old step 3, the rest of this hunk is just renumbering. Shown more clearly on the command line:

$ git show --word-diff origin/pr/732
…
3.[-Once the container is created additional actions MAY be performed based on the features the runtime chooses to support.-]
[-   However, some actions might only be available based on the current state of the container (e.g. only available while it is started).-]
[-4.-] Runtime's [`start`](runtime.md#start) command is invoked with the unique identifier of the container.
[-5.-]{+4.+} The [prestart hooks](config.md#prestart) MUST be invoked by the runtime.
   If any prestart hook fails, the runtime MUST [generate an error](#errors), stop the container, and continue the lifecycle at step [-10.-]
[-6.-]{+9.+}
{+5.+} The runtime MUST run the user-specified program, as specified by [`process`](config.md#process).
[-7.-]{+6.+} The [poststart hooks](config.md#poststart) MUST be invoked by the runtime.
   If any poststart hook fails, the runtime MUST [log a warning](#warnings), but the remaining hooks and lifecycle continue as if the hook had succeeded.
[-8.-]{+7.+} The container process exits.
   This MAY happen due to erroring out, exiting, crashing or the runtime's [`kill`](runtime.md#kill) operation being invoked.
[-9.-]{+8.+} Runtime's [`delete`](runtime.md#delete) command is invoked with the unique identifier of the container.
[-10.-]{+9.+} The container MUST be destroyed by undoing the steps performed during create phase (step 2).
[-11.-]{+10.+} The [poststop hooks](config.md#poststop) MUST be invoked by the runtime.
    If any poststop hook fails, the runtime MUST [log a warning](#warnings), but the remaining hooks and lifecycle continue as if the hook had succeeded.
…

[tianon]

IMO GitHub's "rendered" version makes it even more clear:

[wking]

Rebased and dropped the jumping paragraph with 78e15a9 → ccbc57f. @crosbymichael volunteered to follow up with better wording for that idea.

[tianon]

LGTM

[crosbymichael]

LGTM