[TIZEN MOBILE] Drop XI21 hack.

Tizen IVI does not use XInput, and Tizen 3.0 supports XInput2.2, so
enable_xi21_mt=1 and use_xi2_mt=0 aren't needed anymore.
Merge pull request #1750 from ds-hwang/drop_xi21

[TIZEN MOBILE] Drop XI21 hack.