Revert "Re-apply 4b6c2cd642 "Deferred Concept Instantiation Implementation"""

This reverts commit a9789910.

The patch caused some problems with the libc++ `__range_adaptor_closure`
that I haven't been able to figure out the cause of, so I am reverting
while I figure out whether this is a solvable problem/issue with the
  CFE, or libc++ depending on an older 'incorrect' behavior.