[ownership] Get rid of old entrypoint for creatingEndBorrow that takes the original value.

The original design was to make it so that end_borrow tied at the use level its
original/borrowed value. So we would have:

```
%borrowedVal = begin_borrow %original
...
end_borrow %borrowedVal from %original
```

In the end we decided not to use that design and instead just use:

```
%borrowedVal = begin_borrow %original
...
end_borrow %borrowedVal
```

In order to enable that transition, I left the old API for end_borrow that took
both original and borrowedVal and reimplemented it on top of the new API that
just took the borrowedVal (i.e. the original was just a dead arg).

Now given where we are in the development, it makes sense to get rid of that
transition API and move to just use the new API.

lib/SILGen/SILGenLValue.cpp

@@ -3711,7 +3711,7 @@ static SILValue emitLoadOfSemanticRValue(SILGenFunction &SGF,
     if (!isTake) {                                                             \
       SILValue value = SGF.B.createLoadBorrow(loc, src);                       \
       SILValue strongValue = SGF.B.createStrongCopy##Name##Value(loc, value);  \
-      SGF.B.createEndBorrow(loc, value, src);                                  \
+      SGF.B.createEndBorrow(loc, value);                                       \
       return strongValue;                                                      \
     }                                                                          \
     /* Otherwise perform a load take and destroy the stored value. */          \