Recommend using compileOnly rather than the propdeps plugin

Closes gh-12573

Author: wilkinsona

spring-boot-docs/src/main/asciidoc/appendix-configuration-metadata.adoc

@@ -731,13 +731,12 @@ an optional dependency, for example with Maven you would add:
 	</dependency>
 ----
 
-With Gradle, you can use the https://github.com/spring-gradle-plugins/propdeps-plugin[propdeps-plugin]
-and specify:
+With Gradle you would add:
 
 [source,groovy,indent=0,subs="verbatim,quotes,attributes"]
 ----
 	dependencies {
-		optional "org.springframework.boot:spring-boot-configuration-processor"
+		compileOnly "org.springframework.boot:spring-boot-configuration-processor"
 	}
 
 	compileJava.dependsOn(processResources)

spring-boot-docs/src/main/asciidoc/index.adoc

@@ -47,7 +47,6 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :spring-data-mongo-javadoc: http://docs.spring.io/spring-data/mongodb/docs/current/api/org/springframework/data/mongodb
 :spring-data-rest-javadoc: http://docs.spring.io/spring-data/rest/docs/current/api/org/springframework/data/rest
 :gradle-userguide: http://www.gradle.org/docs/current/userguide
-:propdeps-plugin: https://github.com/spring-projects/gradle-plugins/tree/master/propdeps-plugin
 :ant-manual: http://ant.apache.org/manual
 :code-examples: ../java/org/springframework/boot
 :test-examples: ../../test/java/org/springframework/boot

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -772,17 +772,15 @@ devtools support, simply add the module dependency to your build:
 [source,groovy,indent=0,subs="attributes"]
 ----
 	dependencies {
-		compile("org.springframework.boot:spring-boot-devtools")
+		compileOnly("org.springframework.boot:spring-boot-devtools")
 	}
 ----
 
 NOTE: Developer tools are automatically disabled when running a fully packaged
 application. If your application is launched using `java -jar` or if it's started using a
 special classloader, then it is considered a "`production application`". Flagging the
-dependency as optional is a best practice that prevents devtools from being transitively
-applied to other modules using your project. Gradle does not support `optional`
-dependencies out-of-the-box so you may want to have a look to the
-{propdeps-plugin}[`propdeps-plugin`] in the meantime.
+dependency as optional in Maven or using `compileOnly` in Gradle is a best practice that
+prevents devtools from being transitively applied to other modules using your project.
 
 TIP: repackaged archives do not contain devtools by default. If you want to use
 <<using-boot-devtools-remote,certain remote devtools feature>>, you'll need to disable the