Get rid of a useless helper method in the register allocator.

Get rid of a useless helper method in the register allocator.

Reading the virtual register from a LOperand is only needed used for
unallocated LOperands (LUnallocated). There is no need for having a
method for that on LOperand.
Committed: http://code.google.com/p/v8/source/detail?r=10555

[fschneider, 2012-01-30 14:29:33]

This is a first part of a larger refactoring of LOperands...

[Vyacheslav Egorov (Chromium), 2012-01-30 14:45:00]

lgtm