gh-89532: Remove LibreSSL workarounds (#28728)

Remove LibreSSL specific workaround ifdefs from `_ssl.c` and delete the non-version-specific `_ssl_data.h` file (relevant for OpenSSL < 1.1.1, which we no longer support per PEP 644).

Co-authored-by: Christian Heimes <christian@python.org>
Co-authored-by: Gregory P. Smith <greg@krypto.org>