[std.algorithm.mutation.move] Incorrect documentation

[ichordev]

std.algorithm.mutation.move's documentation says this:

Preconditions
If source has internal pointers that point to itself and doesn't define opPostMove, it cannot be moved, and will trigger an assertion failure.

This mechanism has been commented out for years (what is opPostMove even? A D1 feature?), and may give users of this function a false sense of security. This documentation is also mirrored here:
https://dlang.org/phobos/core_lifetime.html#.move

[Herringway]

Added by #7075. Apparently related to https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1014.md
Seems to be abandoned.