Remove dependency to pageinspect in recovery tests

Remove dependency to pageinspect in recovery tests

If contrib/pageinspect is not installed, this causes the test checking
the minimum recovery point to fail.  The point is that the dependency
with pageinspect is not really necessary as the test does also all
checks with an offline cluster by scanning directly the on-disk pages,
which is enough for the purpose of the test.

Per complaint from Tom Lane.

Author: Michael Paquier
Discussion: https://postgr.es/m/17806.1555566345@sss.pgh.pa.us