Remove get_super_admin grouping from RestrictedFunctions

[rebeccahum]

No need to flag for super admin on VIP Go:

VIP-Coding-Standards/WordPressVIPMinimum/Sniffs/Functions/RestrictedFunctionsSniff.php

Lines 53 to 59 in 6d3f526

	'get_super_admins' => [
	'type' => 'error',
	'message' => '`%s` is prohibited on the WordPress.com VIP platform.',
	'functions' => [
	'get_super_admins',
	],
	],

Silenced here anyways:

VIP-Coding-Standards/WordPress-VIP-Go/ruleset.xml

Lines 305 to 307 in 6d3f526

	<rule ref="WordPressVIPMinimum.Functions.RestrictedFunctions.get_super_admins_get_super_admins">
	<severity>0</severity>
	</rule>

[jrfnl]

Same as for #614:

Loosely related to #600.

The difference between #600 and these changes, is that these are not breaking changes as no sniffs are removed, only error codes (and groups).

This means that this change might make some inline ignore annotations redundant and possibly make some values in custom properties in rulesets redundant, but other than that, it will not break rulesets and it will not break runs.

In other words, these changes are "allowed" to go into a next minor and don't need to wait for the next major (though a choice can be made to let this wait for the next major anyway).