pgsql: Revert "Improve error message on snapshot import in snapmgr.c"

Revert "Improve error message on snapshot import in snapmgr.c"

This reverts commit a0d87bcd9b57, following a remark from Andres Frend
that the new error can be triggered with an incorrect SET TRANSACTION
SNAPSHOT command without being really helpful for the user as it uses
the internal file name.

Discussion: https://postgr.es/m/20230914020724.hlks7vunitvtbbz4@awork3.anarazel.de
Backpatch-through: 11

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/50d44c16335241ccf48c3814fb6cd584be300c09

Modified Files
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src/backend/utils/time/snapmgr.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)