1.0.25.31: axe GC-{ON,OFF}

1.0.25.31: axe GC-{ON,OFF}

... because they are broken, nobody uses them (?), and complicated to
fix.

Rationale:

- There is no way to safely allow gc in a WITHOUT-GCING without making
it entirely useless (nothing like the interrupt protocol with
ALLOW-WITH-INTERRUPTS).

- WITHOUT-GCING implies WITHOUT-INTERRUPTS because interrupts running
with gc disabled may lead to deadlocks (see internals manual on lock
ordering and WITHOUT-GCING) or running out of memory. To adhere to
this contract GC-{ON,OFF} would need to enable/disable interrupts by
setting *INTERRUPTS-ENABLED*, comlicated business for little gain.