pgsql: Revert recent ill-advised test case changes.

Revert recent ill-advised test case changes.

Commit 6bf5c42b5546984df29289918f952e6211069c54 cannot work on Windows,
because it lacks symlink support. While the bug fix in commit
cd64dc42d1e1b03e57e6ba3d316e4f9dec52a78d is correct as far as I know,
the test case changes depend on the previous commit, so this will
have to live without test coverage until we can come up with a better
solution. Commit fa7036dd6644d13233b475874a94754a5903e35a was a test
case bug fix on top of those two, to prevent failures on Linux, so that
has to come out as well.

Per the buildfarm, CI, and Thomas Munro.

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/82023d47de9e262730b1f9b4ea77fae201a89d0a

Modified Files
--------------
src/bin/pg_basebackup/t/010_pg_basebackup.pl      | 21 ++++-
src/bin/pg_combinebackup/t/002_compare_backups.pl | 32 +-------
src/test/perl/PostgreSQL/Test/Cluster.pm          | 93 ++---------------------
3 files changed, 28 insertions(+), 118 deletions(-)