Decorated commands no longer take command_name

Prior to the (sync|async)_command decorators, extension methods had to
construct command results themselves, which required that they have
the name of the command being executed.

When the async_command decorator was introduced, we wanted to maintain
the current command interface, so that a command could be made
asynchronous simply by adding the decorator.

The introduction of the sync_command decorator allows us to satisfy
this objective, without requiring decorated methods to accept a
command_name. This patch modifies both decorators to no longer pass
the command_name argument, and modifies existing command methods not
to expect one.

Closes-Bug: #1308021
Change-Id: I1b33bb7519588cdcb79c6f4d2b10c1e5e8c0cca3
Merge "Decorated commands no longer take command_name"