greybus: loopback: drop dependency on internal timestamps

This patch drops tracking of internal latencies, it's possible to derive
these times via kernel tracepoints and some user-space scripting. Since
there's no other use of the internal timestamp than the loopback driver we
remove the connection.c, connection.h, es1.c, es2.c and loopback.c
inter-dependency in one go.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>