doc/man7/openssl-env: reword the description

doc/man7/openssl-env: reword the description

The manual page describes not only environment variables that pertain
the library, but some of the applications as well (OPENSSL,
OPENSSL_CONFIG, and TSGET are possible examples).  Also, the effect
of the variables is not limited to the changes in default paths.

Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/28025)