pgsql: Reword user-facing message for "power of two"

Reword user-facing message for "power of two"

While there are numerous instances of using "power of 2" in the code,
translated user-facing messages use "power of two". Fix two instances
which used "power of 2" instead.

This is a backpatch of 95fff2abee in master.

Author: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20230829.175615.682972421946735863.horikyota.ntt@gmail.com
Backpatch-through: v16

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/cd59fcff256d68e028bf8a181d4e166e81b6474b

Modified Files
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src/bin/initdb/initdb.c           | 2 +-
src/bin/pg_resetwal/pg_resetwal.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)