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_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/1988f8766eeb297d7867e92bcfdea2e4ff894cc7

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