Cleanup dependencies – disable unnecessary or unused features (#407)

* Disable unnecessary features of config crate, keep only toml

The atuin documentation only mentions the TOML format for configuration
files, but the config crate supports many other formats by default,
which increases the binary size by about 300 kiB.

* Disable unused features of cli-table crate

This doesn't seem to have noticeable effect on the binary size, but
disabling them cleans up the dependency tree a bit.