Remove last_open_read memory cache feature

[masaori335]

@zwoop pointed out the last_open_read cache feature is actually meaning less in 2026 at #13061. Do we want remove it by ATS 11.0.0? IMO, this is one of features makes Stripe complicated, so if possible, I'd remove it.

#13061 (comment)

trafficserver/src/iocore/cache/CacheVC.cc

Lines 476 to 484 in 395bbaf

	// 2. check last open read cache
	if (load_from_last_open_read_call()) {
	Dbg(dbg_ctl_cache_ram, "last open read hit");
	f.doc_from_ram_cache = true;
	io.aio_result = io.aiocb.aio_nbytes;
	POP_HANDLER;
	return EVENT_RETURN;
	}

trafficserver/src/iocore/cache/CacheVC.cc

Lines 532 to 542 in 395bbaf

	bool
	CacheVC::load_from_last_open_read_call()
	{
	if (*this->read_key == this->stripe->first_fragment_key && dir_offset(&this->dir) == this->stripe->first_fragment_offset) {
	this->buf = this->stripe->first_fragment_data;
	ts::Metrics::Counter::increment(cache_rsb.last_open_read_hits);
	ts::Metrics::Counter::increment(stripe->cache_vol->vol_rsb.last_open_read_hits);
	return true;
	}
	return false;
	}

[zwoop]

Yeah, I think we should remove it for v11. +1!