Change test_profile to only compare data that originates from the test file.

Including the full output becomes hairy in the face of the I/O system being
written in Python and thus profiled (i.e., running the test on its own and then
under regrtest created a different profile thanks to an extra flush() call in
the latter case).

No need to backport as 2.x's I/O is entirely C-based and thus not profiled.