pgsql: README: remove duplicate download link & mention related softw.

README: remove duplicate download link & mention related softw.

Reported-by: Daniel Westermann

Discussion: /messages/by-id/DB6PR0902MB2184F7965C9EA9070ACFCA43D2A80@DB6PR0902MB2184.eurprd09.prod.outlook.com

Backpatch-through: master

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0ccb657a3378f6a9b760a2f25dd6f26cb726cf57

Modified Files
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README | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)