pgsql: Revert "Avoid spurious deadlocks when upgrading a tuple lock"

Revert "Avoid spurious deadlocks when upgrading a tuple lock"

This reverts commits 3da73d6839dc and de87a084c0a5.

This code has some tricky corner cases that I'm not sure are correct and
not properly tested anyway, so I'm reverting the whole thing for next
week's releases (reintroducing the deadlock bug that we set to fix).
I'll try again afterwards.

Discussion: https://postgr.es/m/E1hbXKQ-0003g1-0C@gemulon.postgresql.org

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/93d4484ef80aa4df04f70348fd34d45d2eb85416

Modified Files
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src/backend/access/heap/README.tuplock | 10 --
src/backend/access/heap/heapam.c | 83 +++---------
.../expected/tuplelock-upgrade-no-deadlock.out | 150 ---------------------
src/test/isolation/isolation_schedule | 1 -
.../specs/tuplelock-upgrade-no-deadlock.spec | 57 --------
5 files changed, 21 insertions(+), 280 deletions(-)