remoteproc: remove the get_by_name/put API

Remove rproc_get_by_name() and rproc_put(), and the associated
remoteproc infrastructure that supports it (i.e. klist and friends),
because:

1. No one uses them
2. Using them is highly discouraged, and any potential user
   will be deeply scrutinized and encouraged to move.

If a user, that absolutely can't live with the direct boot/shutdown
model, does show up one day, then bringing this functionality back
is going to be trivial.

At this point though, keeping this functionality around is way too
much of a maintenance burden.

Cc: Sjur Brændeland <sjur.brandeland@stericsson.com>
Cc: Loic Pallardy <loic.pallardy@stericsson.com>
Cc: Ludovic BARRE <ludovic.barre@stericsson.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Fernando Guzman Lugo <fernando.lugo@ti.com>
Cc: Suman Anna <s-anna@ti.com>
Cc: Mark Grosen <mgrosen@ti.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>