Revert "Loop if necessary when reading"

This reverts commit aed4a7cc3956c3dfaefb96ac8eb5a09132c61c84.
Limit mmap records to the data actually available

When recording mmap(), the backing file may be smaller than the
requested map size. Conversely, the amount of data mapped may be
smaller than the file size... So we cap the size to record to the
smaller of the amount requested and the amount left in the file (size
minus offset).

Signed-off-by: Stephen Kitt <steve@sk2.org>