pgsql: Get rid of the separate serial_schedule list of tests.

Get rid of the separate serial_schedule list of tests.

Having to maintain two lists of regression test scripts has proven
annoyingly error-prone. We can achieve the effect of the
serial_schedule by running the parallel_schedule with
"--max_connections=1"; so do that and remove serial_schedule.

This causes cosmetic differences in the progress output, but it
doesn't seem worth restructuring pg_regress to avoid that.

Discussion: /messages/by-id/899209.1620759506@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1df3555acc78dedc3ca25eb5e83649b3da1f298f

Modified Files
--------------
src/test/regress/GNUmakefile | 6 +-
src/test/regress/serial_schedule | 212 ---------------------------------------
src/tools/msvc/vcregress.pl | 12 +++
3 files changed, 15 insertions(+), 215 deletions(-)