pg_upgrade: Remove check for pg_config
pg_upgrade: Remove check for pg_config

It is no longer used, but was still being checked for.

bug #7548 from Reinhard Max

snaga/postgres-xl,snaga/postgres-xl,kmjungersen/PostgresXL,postmind-net/postgres-xl,postmind-net/postgres-xl,snaga/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl,kmjungersen/PostgresXL,kmjungersen/PostgresXL,kmjungersen/PostgresXL,snaga/postgres-xl,postmind-net/postgres-xl,arcivanov/postgres-xl,postmind-net/postgres-xl,arcivanov/postgres-xl,arcivanov/postgres-xl,snaga/postgres-xl,arcivanov/postgres-xl,kmjungersen/PostgresXL,arcivanov/postgres-xl