Remove deprecated Event Watcher configration in .pipe dir

[ffjlabo]

What would you like to be added:

Why is this needed:

[t-kikuc]

Let's deprecate this feature. The process may be (the version is not determined):

1. Announce the future deprecation when releasing v0.49.0
2. Remove code&docs in v0.50.0

I thinks the change will be like this:

• code: b768554
• docs: bc48112

[t-kikuc]

First of all, let's show warning log 👍 See #5168

[t-kikuc]

We will not deprecate the feature for some months.
We need to focus on the plugin.