Remove redundant deprecated attribute

The `deprecated` attribute is deprecated as of Spring Boot 1.3 and
replaced by the `deprecation` object. Any IDE relying on the previous
structure still expects the `deprecated` attribute though.

The annotation processor is adding that information automatically when it
merges manual content so it is not necessary to define that attribute in
the source.

Closes gh-4127

spring-boot/src/main/resources/META-INF/additional-spring-configuration-metadata.json

@@ -122,7 +122,6 @@
     "sourceType": "org.springframework.boot.SpringApplication",
     "description": "Display the banner when the application runs.",
     "defaultValue": true,
-    "deprecated": true,
     "deprecation": {"replacement": "spring.main.banner-mode"}
   },
   {