chore(core): delete duplicated file. (#1940)

**Motivation**
This file appears twice, once as Clippy.toml and once as clippy.toml

> warning: the following paths have collided (e.g. case-sensitive paths
> on a case-insensitive filesystem) and only one from the same
> colliding group is in the working tree:
> 
>   'crates/l2/Clippy.toml'
>   'crates/l2/clippy.toml'