MdePkg: backout Ipmi2.0 definitions header file.

MdePkg: backout Ipmi2.0 definitions header file.

The file name is too long and with "Definitions" word
that is duplicated meanings for the header file.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Daocheng Bu <daocheng.bu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19231 6f19259b-4bc3-4df7-8a09-765794883524