Remove duplicated endraw statement for documentation generation (#2589)

* Remove duplicated endraw statement for documentation generation

This was accidentally copy pasted in my last PR, breaking documentation generation.

#2578

* Remove proto3 reference for code block

* Fix code block format

* proto -> protobuf

Author: BCook98

docs/docs/mapping/customizing_openapi_output.md

@@ -283,7 +283,6 @@ Output json:
     ]
 },
 ```
-{% endraw %}
 
 ### Hiding fields, methods, services and enum values
 
@@ -317,7 +316,7 @@ Note: Annotations are only supported on Services, Methods, Fields and Enum Value
 `opt: visibility_restriction_selectors=PREVIEW` will result in:
 
 Input Example:
-```proto3
+```protobuf
 service Echo {
     rpc EchoInternal(VisibilityRuleSimpleMessage) returns (VisibilityRuleSimpleMessage) {
         option (google.api.method_visibility).restriction = "INTERNAL";