OMETIFFFormat: remove unnecessary static services

the OMEXML and OMEXMLMetadata services were static for no reason, as
they can be automatically populated via context injection (and there was
no reason to null them on closing).

This also removes completely unnecessary service creation logic.
OMEXMLServiceImpl: correct annotation type

Should be indexed on Service.class.
OMETIFFFormat: remove shadowed service variable

The service variable was duplicated in the Writer class, and the Format.
Just leave it declared in the Format and discovered once on Format
creation.