Revert "net: Introduce net.ipv4.tcp_migrate_req."

This reverts commit cf6c06ac which is
commit f9ac779f upstream.

It breaks the Android abi.  If it is required in the future, it can come
back in an abi-safe way.

Bug: 161946584
Change-Id: Ia4d18c9acdd553b1806ca844c47e34a76f6c6b93
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>