Revert "coredump: Snapshot the vmas in do_coredump"

This reverts commit f6ca8628.

It breaks the kernel abi so revert it for now.  We will add it back
later at the next kabi update.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ie2c8d32fbcab4289c1087ebfee3c1106cd637eef