fixes doc linting error: redundant explicit link target

[nsipplswezey]

API doc build job errors on redundant explicit target.
This removes the redundant explicit target, and passes CI doc build.

error: redundant explicit link target
  --> scylla/src/lib.rs:16:55
   |
16 | //! All driver activity revolves around the [Session](crate::Session)\
   |                                                                          -------  ^^^^^^^^^^^^^^ explicit target is redundant
   |                                                                          |
   |                                                                          because label contains path that resolves to same destination
   |
   = note: when a link's destination is not specified,
           the label is used to resolve intra-doc links
   = note: `-D rustdoc::redundant-explicit-links` implied by `-D warnings`
help: remove explicit link target

fixes: #847

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• [-] I have provided docstrings for the public items that I want to introduce.
• [-] I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[piodul]

LGTM, thanks.