Callers of InitFromFilePart log the error and exit.
It is better to log the error with the path to the part and the call stack
directly inside the MustInitFromFilePart() function.
This simplifies the code at callers' side while leaving the same level of debuggability.
This reverts commit bab6a15ae0.
Reason for revert: the `fetchData` arg is used in cluster branch.
Leaving this arg in master branch makes smaller the diff with cluster branch.
This eliminates the need for storing block data into temporary files on a single-node VictoriaMetrics
during heavy queries, which touch big number of time series over long time ranges.
This improves single-node VM performance on heavy queries by up to 2x.
