A quick check of Apple’s online store suggests the company is quickly selling through its remaining stock of clearance and refurbished first-generation iPad units. Among the new, clearance-priced stock, the company is completely out of Wi-Fi only units, although it does show stock of all three capacities of Wi-Fi + 3G models. Apple also appears to be out of refurbished 16GB Wi-Fi units; Boy Genius Report suggests that the company’s stock…