removing a bundle from an entity when one of the component has already been removed crashes

[mockersf]

On bevy master, , when removing a bundle from an entity when one of the component has already been removed, it crashes with this unwrap: https://github.com/bevyengine/bevy/blob/master/crates/bevy_ecs/src/system/commands.rs#L150

When using remove_one instead of remove to remove a component, it never crashes even if the component is not present on the entity. This is because remove_one checks for the presence of the component before removing it: https://github.com/bevyengine/bevy/blob/master/crates/bevy_ecs/src/system/commands.rs#L129

In the spirit of #649 and #651, I was thinking of removing the unwrap with a log, but that would mean that the other remaining components from the bundle won't be removed which may be an unexpected behaviour for the user.

The other way around this would be, when a bundle fails to remove, to try to remove each component of the bundle one by one, but I'm not sure if that's a good fix...

What do you think?

example code to reproduce the issue

remove_tag1 will never fail even though it just removes Tag1 from every entity, remove_tag12 will crash one Tag1 are removed.

use bevy::prelude::*;

struct Tag1;
struct Tag2;

fn main() {
    App::build()
        .add_default_plugins()
        .add_startup_system(startup_system.system())
        .add_system(count.system())
        .add_system(remove_tag1.system())
        .add_system(remove_tag12.system())
        .run();
}

fn startup_system(mut commands: Commands) {
    println!("setup");
    commands.spawn((Tag1, Tag2));
    commands.spawn((Tag1,));
}

fn count(mut tag1_query: Query<&Tag1>, mut tag2_query: Query<&Tag2>) {
    println!("counting tags");
    println!("- tag1 count: {}", tag1_query.iter().iter().len());
    println!("- tag2 count: {}", tag2_query.iter().iter().len());
}

fn remove_tag1(mut commands: Commands, mut entity_query: Query<Entity>) {
    let mut removed = 0;
    for entity in &mut entity_query.iter() {
        commands.remove_one::<Tag1>(entity);
        removed += 1;
    }
    println!("removed {} Tag1", removed);
}

fn remove_tag12(mut commands: Commands, mut entity_query: Query<(Entity, &Tag2)>) {
    let mut removed = 0;
    for (entity, _tag2) in &mut entity_query.iter() {
        commands.remove::<(Tag1, Tag2)>(entity);
        removed += 1;
    }
    println!("removed {} Tag1 & Tag2", removed);
}

[CleanCut]

Here's my take at fixing the situation: #710