pgsql: Update reference to sampling algorithm in analyze.c

Update reference to sampling algorithm in analyze.c

Commit 83e176ec1 moved row sampling functions from analyze.c to
utils/misc/sampling.c, but failed to update comment referring to
the sampling algorithm from Jeff Vitter's paper. Correct the
comment by pointing to utils/misc/sampling.c.

Author: Etsuro Fujita
Discussion: https://postgr.es/m/CAPmGK154gp%2BQd%3DcorQOv%2BPmbyVyZBjp_%2Bhb766UJeD1e_ie6XQ%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/69fd82fedd746b82427097883daf2921dd77584e

Modified Files
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src/backend/commands/analyze.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)