tracker-miner-fs: Always delete graph nie:InformationElement on create/update

There are some situations where the file monitors cannot distinguish between a file being created where none existed before, or a file newly created replacing a previously existing file.

Treat all create/update events the same WRT trimming the previously existing nie:InformationElements, in order to ensure these updates that pass as creates also result in the file being reindexed by the metadata extractor. This only applies to files that would have metadata extracted.

While at it, simplify the SPARQL and move the code so that it is not scattered across the function.