Remove user_meta related sniffs

[rebeccahum]

User meta is easily accessible on VIP Go, no reason to have the user_meta grouping in the RestrictedFunctions sniff:

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

Lines 132 to 141 in 6d3f526

	'user_meta' => [
	'type' => 'error',
	'message' => '%s() usage is highly discouraged on WordPress.com VIP due to it being a multisite, please see https://lobby.vip.wordpress.com/wordpress-com-documentation/code-review-what-we-look-for/#wp_users-and-user_meta.',
	'functions' => [
	'get_user_meta',
	'update_user_meta',
	'delete_user_meta',
	'add_user_meta',
	],
	],

We silence it anyways on the WordPress-VIP-Go ruleset:

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

Lines 281 to 290 in 6d3f526

	<rule ref="WordPressVIPMinimum.Functions.RestrictedFunctions.user_meta_add_user_meta">
	<severity>0</severity>
	</rule>
	<rule ref="WordPressVIPMinimum.Functions.RestrictedFunctions.user_meta_delete_user_meta">
	<severity>0</severity>
	</rule>
	<rule ref="WordPressVIPMinimum.Functions.RestrictedFunctions.user_meta_get_user_meta">
	<severity>0</severity>
	</rule>
	<rule ref="WordPressVIPMinimum.Functions.RestrictedFunctions.user_meta_update_user_meta">

The same could be said for the RestrictedVariables sniff:

VIP-Coding-Standards/WordPressVIPMinimum/Sniffs/Variables/RestrictedVariablesSniff.php

Lines 41 to 47 in 6d3f526

	'user_meta' => [
	'type' => 'error',
	'message' => 'Usage of users/usermeta tables is highly discouraged in VIP context, For storing user additional user metadata, you should look at User Attributes.',
	'object_vars' => [
	'$wpdb->users',
	'$wpdb->usermeta',
	],

Silenced on the same ruleset:

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

Lines 293 to 295 in 6d3f526

	<rule ref="WordPressVIPMinimum.Variables.RestrictedVariables.user_meta__wpdb__usermeta">
	<severity>0</severity>
	</rule>

[jrfnl]

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).

[jrfnl]

I have prepared the commits for this. @rebeccahum Let me know if you want me to pull these changes now or when we're preparing for v3.0.

[rebeccahum]

@jrfnl Please pull the changes now. Thank you!