Remove redundant `is_multisite()` checks in network admin templates

[flixos90]

Most of the templates for the network admin have a check for is_multisite() in the beginning of the file. However there's already such a check happening in the admin.php file for the network admin, making these additional checks redundant. Let's remove them.

[flixos90]

37447.diff​ removes all the unnecessary is_multisite() checks.

[SergeyBiryukov]

Originally introduced in [12609], expanded in [16272]. network/admin.php was added in [15481].

Looking at [16272], I guess the checks are there just in case the one in network/admin.php gets removed at some point (it might be an oversight as well, but seems unlikely).

[flixos90]

Replying to SergeyBiryukov:

Looking at [16272], I guess the checks are there just in case the one in network/admin.php gets removed at some pount (it might be an oversight as well, but seems unlikely).

Why would that file be removed? Solely for that purpose, (so that we don't need duplicate code) I think it would make sense to keep it.

[swissspidy]

Replying to flixos90:

Replying to SergeyBiryukov:

Looking at [16272], I guess the checks are there just in case the one in network/admin.php gets removed at some pount (it might be an oversight as well, but seems unlikely).

Why would that file be removed? Solely for that purpose, (so that we don't need duplicate code) I think it would make sense to keep it.

Not the file could be removed, but the checks in it.

[jeremyfelt]

I think we're okay to remove these. It seems (IMO) like part of [16272] was about applying some consistency to network admin files that didn't have both the is_multisite() check and the bootstrap documentation. It doesn't really hurt to to have the 2 checks, but the opportunity to reduce code is nice. :)

Is there a way we can work in a one line comment above the check in wp-admin/network/admin.php to clarify its importance?

[flixos90]

Replying to jeremyfelt:

Is there a way we can work in a one line comment above the check in wp-admin/network/admin.php to clarify its importance?

I added such a note in 37447.2.diff​.

[johnjamesjacoby]

This looks OK to me.

[jeremyfelt]

In 38657:

Multisite: Remove redundant is_multisite() checks in network admin templates.

wp-admin/network/admin.php is required by all of the individual network templates and begins with an is_multisite() check of its own. Because of this, we can remove the 26 other checks in the individual templates.

Props flixos90.
Fixes #37447.