Revert "configure: check for socat and its escape feature"

This reverts commit 37fc2cf5, since it
introduces configure.ac changes that depend on very very new autoconf
macros that are not present in current stable distros (and it was not
advertised as such).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>