Revert "printk: declare printk_deferred_{enter,safe}() in include/linux/printk.h"

This reverts commit 32232bcd.

The support for deferred printing was removed in v5.10-rc1-rt1 by commit
9153e3c5cb0c9 ("printk: remove deferred printing") because:

    Since printing occurs either atomically or from the printing
    kthread, there is no need for any deferring or tracking possible
    recursion paths. Remove all printk context tracking.

Fixes: 32232bcd ("printk: declare printk_deferred_{enter,safe}() in include/linux/printk.h")
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>