deps: replace plotlib used by risingwave_bench

[xiangjinwu]

The plotlib crate (introduced by #17463) has not been updated for more than 4 years, and has several issues:

Depending on old version of svg crate:

warning: the following packages contain code that will be rejected by a future version of Rust: svg v0.7.2
note: to see what the problems were, use the option `--future-incompat-report`, or run `cargo report future-incompatibilities --id 1`

Depending on another crate failure dead for 4 years:
https://github.com/risingwavelabs/risingwave/security/dependabot/173
https://github.com/risingwavelabs/risingwave/security/dependabot/174