This commit removes the WITH_SSL=<custom_location_of_openssl> option,
leaving only -DWITH_SSL=bundled/system.

The rationale behind this removal is as follows:

1. The WITH_SSL=<custom_location_of_openssl> option is obscure
and not widely used.

2. There is no added value in this option compared to using
OPENSSL_ROOT_DIR. In fact, the availability of "helpful" MySQL options
might discourage users from exploring proper CMake options independently.

3. Users may incorrectly assume full MySQL compatibility even with this
option, including undocumented behaviors such as MySQL's preference for static libraries
with WITH_SSL=<custom_location_of_openssl>.

This change simplifies the configuration options and encourages users to
adopt more standardized and documented practices.