Having RHSKnownZero and RHSKnownOne be alternative names for KnownZero and KnownOne

Having RHSKnownZero and RHSKnownOne be alternative names for KnownZero and KnownOne
(via APInt &RHSKnownZero = KnownZero, etc) seems dangerous and confusing to me: it
is easy not to notice this, and then wonder why KnownZero/RHSKnownZero changed
underneath you when you modified RHSKnownZero/KnownZero etc.  So get rid of this.
No intended functionality change (tested with "make check" + llvm-gcc bootstrap).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94802 91177308-0d34-0410-b5e6-96231b3b80d8