Revert "Tidy up locale thread safety in ECPG library."
This reverts commit
8e993bff5326b00ced137c837fce7cd1e0ecae14.
It causes various build failures on the buildfarm, to be investigated.
Discussion: https://postgr.es/m/CWZBBRR6YA8D.8EHMDRGLCKCD%40neon.tech