Update AV1800 guideline (#375)

Split from #298.

Co-authored-by: Dennis Doomen <dennis.doomen@greenchoice.nl>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

_rules/1800.md

@@ -5,5 +5,3 @@ title: Consider using `Any()` to determine whether an `IEnumerable<T>` is empty
 severity: 3
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 When a member or local function returns an `IEnumerable<T>` or other collection class that does not expose a `Count` property, use the `Any()` extension method rather than `Count()` to determine whether the collection contains items. If you do use `Count()`, you risk that iterating over the entire collection might have a significant impact (such as when it really is an `IQueryable<T>` to a persistent store).
-
-**Note:** If you return an `IEnumerable<T>` to prevent changes from calling code as explained in [{{ site.default_rule_prefix }}1130](/member-design-guidelines#{{ site.default_rule_prefix }}1130), and you're developing in .NET 4.5 or higher, consider the new read-only classes.