Revert "[libc++] Fix PR35491 - std::array of zero-size doesn't work with...

Revert "[libc++] Fix PR35491 - std::array of zero-size doesn't work with non-default constructible types."
Revert "Fix initialization of array<const T, 0> with GCC."
Revert "Make array<const T, 0> non-CopyAssignable and make swap and fill ill-formed."

This reverts commit r324182, r324185, and r324194 which were causing issues with zero-length std::arrays.

llvm-svn: 324309