refactor: options.pageFormat now uses osmd.setPageFormat, instead of duplicated code
refactor: options.pageFormat now uses osmd.setPageFormat, instead of duplicated code

updated outdated comment, which triggered this change.
before, checking options.pageFormat basically duplicated the code of osmd.setPageFormat, but not entirely.

The change doesn't do functional changes for now, because osmd.needBackendUpdate is currently unused,
but this is cleaner in any case.

opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay