Documentation/kdump/kdump.txt: remove /dev/oldmem description

Documentation/kdump/kdump.txt: remove /dev/oldmem description

Signed-off-by: Zhang Yanfei <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Fenghua Yu <[email protected]>
Cc: Heiko Carstens <[email protected]>
Cc: Martin Schwidefsky <[email protected]>
Cc: Matt Fleming <[email protected]>
Cc: Michael Holzheu <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralf Baechle <[email protected]>
Cc: Tony Luck <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>