err: get rid of err_free_strings_int()

err: get rid of err_free_strings_int()

Even though the function is not part of the public api, it is not
entirely removed, in order to minimize the chance of breakage,
because it is exported from libcrypto. Instead, we keep a dummy
implementation.

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17974)

(cherry picked from commit 1c8787d5e0b01bedfc3cbe5eab5b85290221d8c1)