pgsql: Fix some -Wcast-qual warnings

Fix some -Wcast-qual warnings

Small rearrangements to avoid having to cast away qualifiers. In some
cases, the whole cast was unnecessary.

Reviewed-by: Heikki Linnakangas <hlinnaka(at)iki(dot)fi>
Discussion: https://www.postgresql.org/message-id/flat/459217ca-3840-4452-8cd1-8f9b47e8d479%40eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e58994c30199258c7abfdfd65140a699faac0a1c

Modified Files
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contrib/btree_gist/btree_bit.c | 4 ++--
contrib/btree_gist/btree_utils_var.c | 4 ++--
contrib/btree_gist/btree_utils_var.h | 2 +-
contrib/postgres_fdw/connection.c | 11 ++++++----
contrib/xml2/xslt_proc.c | 15 +++++++-------
src/backend/utils/adt/multirangetypes.c | 6 +++---
src/backend/utils/adt/rangetypes.c | 2 +-
src/backend/utils/adt/varlena.c | 24 +++++++++++-----------
src/include/storage/bufpage.h | 2 +-
.../test_custom_stats/test_custom_var_stats.c | 2 +-
10 files changed, 38 insertions(+), 34 deletions(-)