host-ipmid: ipmid-api: drop extern C linking
host-ipmid: ipmid-api: drop extern C linking

Header not used by any C code at this point, drop extern C linking and
unused headers associated with C compilation.

Change-Id: Icdb1dd220d158256562a2529d9aa7b03ed1e2196
Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>

openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid,openbmc/phosphor-host-ipmid