Drop the CONFIG_KEXEC_CORE #ifdef around reference to "kexec_in_progress".

Commit 2b94ed24 ("kexec: define kexec_in_progress in !CONFIG_KEXEC
case") has made this unnecessary.
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>