proc.5: wfix

proc.5: wfix

In the section for /proc/[pid]/smaps, the description of field
ProtectionKey occurs twice: both before and after the description of
VmFlags.

Changes made by this patch:
1) Only the first occurrence is kept because its order matches the
output of /proc/[pid]/smaps.
2) The kernel version that CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS was
introduced is only mentioned in the second occurrence. Now it's moved
to the first one.

Signed-off-by: Jing Peng <pj.hades@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>