pgsql: pg_resetwal: Use new routine to retrieve data of PG_VERSION

pg_resetwal: Use new routine to retrieve data of PG_VERSION

pg_resetwal's custom logic to retrieve the version number of a data
folder's PG_VERSION can be replaced by the facility introduced in
cd0be131ba6f. This removes some code.

One thing specific to pg_resetwal is that the first line of PG_VERSION
is read and reported in the error report generated when the major
version read does not match with the version pg_resetwal has been
compiled with. The new logic preserves this property, without changes
to neither the error message nor the data used in the error report.

Note that as a chdir() is done within the data folder before checking the
data of PG_VERSION, get_pg_version() needs to be tweaked to look for
PG_VERSION in the current folder.

Author: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Discussion: https://postgr.es/m/aOiirvWJzwdVCXph@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c6a6cd53d3ababa667aa224229550b96fb13cf26

Modified Files
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src/bin/pg_resetwal/pg_resetwal.c | 30 +++++++-----------------------
1 file changed, 7 insertions(+), 23 deletions(-)