chore: remove deprecated --npm flag

[TMisiukiewicz]

Summary:

The --npm flag in init command has been deprecated for more than a year now in favor of using --pm flag. Since npm will become a default package manager when initializing new project (#2503), I think it's a good time to remove this flag.

Test Plan:

1. Run init command locally and use --npm flag
2. Verify error is displayed:

error: unknown option '--npm'
(Did you mean --pm?)

Checklist

• Documentation is up to date to reflect these changes.
• Follows commit message convention described in CONTRIBUTING.md

[szymonrybczak]

Thanks! 🧹

[thymikee]

@cortinico this is a small braking change that shouldn't affect too many users, shall we ship it as a part of 0.76 and document in the changelog?

[szymonrybczak]

@cortinico this is a small braking change that shouldn't affect too many users,

To give more context, this option was deprecated with appropriate warning for 3 major versions already.

[cortinico]

@cortinico this is a small braking change that shouldn't affect too many users, shall we ship it as a part of 0.76 and document in the changelog?

Yup this sounds reasonable 👍