Remove deprecated is_method_error code

The is_method_error() function is no longer needed, instead a
try-catch block should be used instead.
Reference:
https://lists.ozlabs.org/pipermail/openbmc/2018-October/013696.html,

Change-Id: I1919ea33fc18be2b8afd51fb1f85ddef15041e7c
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
2 files changed