crash_dump: remove duplicate include in crash_dump.h

In crash_dump.h, header file <linux/pgtable.h> is included twice.  This
duplication was introduced in commit 65fddcfc("mm: reorder includes
after introduction of linux/pgtable.h") where the order of the header
files is adjusted, while the old one was not removed.

Clean it up here.

Link: https://lkml.kernel.org/r/20211020090659.1038877-1-ye.guojin@zte.com.cn


Signed-off-by: Ye Guojin <ye.guojin@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Changcheng Deng <deng.changcheng@zte.com.cn>
Cc: Simon Horman <horms@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>