pgsql: Upgrade internal error message to external

Upgrade internal error message to external

As part of REINDEX CONCURRENTLY, this formerly internal-only error
message becomes potentially user-visible (see regression tests), so
change from errmsg_internal() to errmsg(), and update comment.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/12e037e2090b1a6446376814ea0419463b02c254

Modified Files
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src/backend/catalog/index.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)