PM / Driver Core: Kill dev_pm_ops platform warning for now

Commit 783ea7d4
(Driver Core: Rework platform suspend/resume, print warning)
added a warning message printed for platform drivers that use the
legacy PM callbacks rather than struct dev_pm_ops.  Unfortunately,
this resulted in some confusion and made some people try to convert
drivers by replacing the old callbacks with struct dev_pm_ops in
automatic way, which generally is not a good idea.

Remove the platform device runtime dev_pm_ops warning for now,
because it's annoying to users and it's not really necessary right
now.

[rjw: Modified the changelog to be more informative.]

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>