Deprecate invariant_booleans (#3497)

* Deprecate invariant_booleans

* all.yaml

* fmt

Author: srawlins

example/all.yaml

@@ -76,7 +76,6 @@ linter:
     - flutter_style_todos
     - hash_and_equals
     - implementation_imports
-    - invariant_booleans
     - iterable_contains_unrelated_type
     - join_return_with_assignment
     - leading_newlines_in_multiline_strings

lib/src/rules/invariant_booleans.dart

@@ -16,6 +16,8 @@ const _desc =
     r'Conditions should not unconditionally evaluate to `true` or to `false`.';
 
 const _details = r'''
+**DEPRECATED:** This rule is unmaintained and will be removed in a future Linter
+release.
 
 **DON'T** test for conditions that can be inferred at compile time or test the
 same condition twice.
@@ -109,9 +111,7 @@ class InvariantBooleans extends LintRule {
             name: 'invariant_booleans',
             description: _desc,
             details: _details,
-            // This rule is experimental until there are fewer "false positive"
-            // bugs, and performance has been improved.
-            maturity: Maturity.experimental,
+            maturity: Maturity.deprecated,
             group: Group.errors);
 
   @override