pgsql: Revert bogus fixes of HOT-freezing bug

Revert bogus fixes of HOT-freezing bug

It turns out we misdiagnosed what the real problem was. Revert the
previous changes, because they may have worse consequences going
forward. A better fix is forthcoming.

The simplistic test case is kept, though disabled.

Discussion: https://postgr.es/m/[email protected]

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/08ba67d596a1443c32d0b5300aaad8042729cd41

Modified Files
--------------
src/backend/access/heap/heapam.c | 109 +++++++---------------------------
src/backend/access/heap/pruneheap.c | 4 +-
src/backend/commands/vacuumlazy.c | 20 +++----
src/backend/executor/execMain.c | 6 +-
src/include/access/heapam.h | 3 -
src/test/isolation/isolation_schedule | 1 -
6 files changed, 38 insertions(+), 105 deletions(-)