Revert "Add an optional parameter with a list of undefs to extendToIndices"

This reverts commit r280268, it causes all MSVC 2013 to ICE. This
appears to have been fixed in a later MSVC 2013 update, because I cannot
reproduce it locally. That said, all upstream LLVM bots are broken right
now, so I am reverting.

Also reverts dependent change r280275, "[Hexagon] Deal with undefs when
extending live intervals".

llvm-svn: 280301