MINOR: pools: drop the unused static history of artificially failed allocs

MINOR: pools: drop the unused static history of artificially failed allocs

When building with DEBUG_FAIL_ALLOC we call a random generator to decide
whether the pool alloc should succeed or fail, and there was a preliminary
debugging mechanism to keep sort of a history of the previous decisions. But
it was never used, enforces a lock during the allocation, and forces to use
static variables, all of which are limiting the ability to pursue the pools
cleanups with no real benefit. Let's get rid of them now.