fix(src/main): There are unused variables and unused import elements

[xuesongbj]

There are unused variables and unused import elements.

$ make debug cargo build Compiling toda v0.2.0 (/home/toda) warning: unused import: Comm --> src/main.rs:43:29 | 43 | use jsonrpc::{start_server, Comm}; | ^^^^ | = note: #[warn(unused_imports)] on by default

warning: unused variable: rx --> src/main.rs:182:14 | 182 | let (tx, rx) = mpsc::channel(); | ^^ help: if this is intentional, prefix it with an underscore: _rx | = note: #[warn(unused_variables)] on by default

warning: 2 warnings emitted

Finished dev [unoptimized + debuginfo] target(s) in 14.78s