Revert "fix wrong bitness detection logic for PyPy"

This reverts commit ce065b493510478f7b8a4fbf2cbde43b664c6ce6.

Upon further comparison, it becomes clear that what we *really* want is *only*
ignoring the symlinking phase but *not* skipping the libXX logic
altogether, like what the previous commit did. Actually since explicit
bitness libdir would only be handled if a `libdir-bitness.txt` is
present, the previous commit would have broken all newly-created PyPy
virtualenv's on explicit bitness libdirs.