doc: `google_re2` for type type.matcher.v3.RegexMatcher is not required any more (#26876)

Related to https://github.com/envoyproxy/envoy/issues/26875

Signed-off-by: Davin Kevin <davin.kevin@gmail.com>

Mirrored from https://github.com/envoyproxy/envoy @ 5e834d0d8d18918beddd4a8f1267f9fda8b49807

envoy/type/matcher/v3/regex.proto

@@ -57,11 +57,8 @@ message RegexMatcher {
 
   oneof engine_type {
     // Google's RE2 regex engine.
-    GoogleRE2 google_re2 = 1 [
-      deprecated = true,
-      (validate.rules).message = {required: true},
-      (envoy.annotations.deprecated_at_minor_version) = "3.0"
-    ];
+    GoogleRE2 google_re2 = 1
+        [deprecated = true, (envoy.annotations.deprecated_at_minor_version) = "3.0"];
   }
 
   // The regex match string. The string must be supported by the configured engine. The regex is matched