TailDuplicator: Remove live-in updating logic

This logic was introduced in r157663 and does not make any sense to me.
The motivating example in rdar://11538365 looks like this:

This is the tail:
BB#16: derived from LLVM BB %if.end68
    Live Ins: %R0 %R4 %R5
    Predecessors according to CFG: BB#15 BB#5
        tBLXi pred:14, pred:%noreg, <ga:@CFRelease>, %R0<kill>, <regmask>, %LR<imp-def,dead>, %SP<imp-use>, %SP<imp-def>
        t2B <BB#20>, pred:14, pred:%noreg
    Successors according to CFG: BB#20

This is the predBB:
BB#5:
    Live Ins: %R5
    Predecessors according to CFG: BB#4
        %R4<def> = t2MOVi 0, pred:14, pred:%noreg, opt:%noreg
        t2B <BB#16>, pred:14, pred:%noreg
    Successors according to CFG: BB#16

However this is invalid machine code to begin with, if %R0 is live-in to
BB#16 then it must be live-in to BB#5 as well if BB#5 does not define
it.  We should not need logic to retroactively fix broken machine code
and in fact the example from r157663 passes cleanly with the code
removed and I do not see any (newly) failing tests with the machine
verifier enabled.

Differential Revision: http://reviews.llvm.org/D22031

llvm-svn: 274655