Get rid of all usages of BR2_RECENT

Since BR2_RECENT was enabled by default, we do not want entries marked
BR2_RECENT (and thus appearing by default in Buildroot) to disappear.

Therefore, all the entries marked BR2_RECENT are converted as
non-deprecated. We can later decide, on a per-entry basis, to add
BR2_DEPRECATED to some of them. But at least, this commit doesn't
change the default current behaviour of Buildroot.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>