Revert "selftest/vm: verify remap destination address in mremap_test"

Revert "selftest/vm: verify remap destination address in mremap_test"

This reverts commit 0b4e16093e081a3ab08b0d6cedf79b249f41b248.

The upstream commit 18d609daa546 ("selftest/vm: verify remap destination
address in mremap_test") was backported as commit 2688d967ec65
("selftest/vm: verify remap destination address in mremap_test").
Repeated backport introduced the duplicate of function
is_remap_region_valid to the file breakign the vm selftest build.

Fixes: 0b4e16093e08 ("selftest/vm: verify remap destination address in mremap_test")
Signed-off-by: Oleksandr Tymoshenko <ovt@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>