pgsql: Remove REGRESS_OUTPUTDIR environment variable.

Remove REGRESS_OUTPUTDIR environment variable.

Andres Freund points out that the tmp_check path is already available as
perl variable PostgreSQL::Test::Utils::tmp_check, so we can drop the new
environment variable introduced by commit f47ed79cc.

Discussion: https://postgr.es/m/20220213052955.dh7lheehit7bsemf%40alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7e6124ca7d81f4767a44bae487226bc8b003ec31

Modified Files
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src/test/recovery/Makefile                | 4 ----
src/test/recovery/t/027_stream_regress.pl | 2 +-
src/tools/msvc/vcregress.pl               | 2 --
3 files changed, 1 insertion(+), 7 deletions(-)