Drop isMethodCacheable check on query alters

Follow-up from #3395776: Make POST requests render cacheable.

Essentially it turned out that adding these checks didn't do anything to begin with On POST requests: We would never get a cache hit, nor set the cache. Now we can get a cache hit, which doesn't run said code or still do not set anything on a cache miss. So worst case scenario the code runs but has no effect. The upside is that if we remove the check and we somehow do end up supporting cache sets on POST (fat chance in hell) that our code won't be insecure. If we leave the check, it will be.