perf(jqLite): simplify jqLiteDealoc

while querySelectorAll is much more expensive than getElementsByTagName on elements with
both many and few children, cloning the live node list returned by getElementsByTagName
makes it as expensive as querySelectorAll (we need to clone because we need the node list
not to change while we iterate over it).

the childNodes and childNodes.length check is as expensive as querySelectorAll on a node
without any children, so it only makes the whole lookup 2x as slow, so I'm removing it.