feature: @putout/plugin-remove-nested-blocks: case when it is the only block

[echo094]

When a block is the only block in its container, this nested block can be removed safely:

let x1;
function fun1(f) {
    {
        let x1 = f;
        return x1;
    }
}

[coderaiser]

Nice! Please run npm run fix:lint in the directory of a plugin to fix linting-related issues.

[coderaiser]

Thank you!