Revert the LSDA change to scan_eh_tab.

This commit reverts the LSDA-related change in r211745.

The r211745 adds a new argument to scan_eh_tab(), i.e. lsda.
However, IMO, calling _Unwind_GetLanguageSpecificData() directly in
scan_eh_tab() was more intuitive and reduces several function call
to _Unwind_GetLanguageSpecificData() in __cxx_personality_v0().