pgsql: Remove unnecessary smgropen() calls

Remove unnecessary smgropen() calls

Now that RelationCreateStorage() returns the SmgrRelation (since
commit 5c1560606dc), use that.

Author: Japin Li
Discussion:
https://www.postgresql.org/message-id/ME3P282MB316600FA62F6605477F26F6AB6742@ME3P282MB3166.AUSP282.PROD.OUTLOOK.COM

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9f35e42e7d59fb8716020a42c7b586f0d70a5101

Modified Files
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src/backend/access/heap/heapam_handler.c | 4 +---
src/backend/commands/tablecmds.c         | 4 +---
2 files changed, 2 insertions(+), 6 deletions(-)