Remove version elements from Maven plugin documentation

This commit removes `<version>` from the Maven Plugin documentation
where it makes sense so that versions aren't hardcoded unnecessarily.

Rather, a plugin or dependency management should be in place so those
are not needed.

Closes gh-23909

spring-boot-project/spring-boot-docs/src/main/asciidoc/build-tool-plugins.adoc

@@ -34,7 +34,6 @@ To use the Spring Boot Maven Plugin, include the appropriate XML in the `plugins
 				<plugin>
 					<groupId>org.springframework.boot</groupId>
 					<artifactId>spring-boot-maven-plugin</artifactId>
-					<version>{spring-boot-version}</version>
 					<executions>
 						<execution>
 							<goals>

spring-boot-project/spring-boot-docs/src/main/asciidoc/deployment.adoc

@@ -435,7 +435,6 @@ You can deploy the app (for example, with a Maven plugin) by adding the project
 	<plugin>
 		<groupId>com.google.cloud.tools</groupId>
 		<artifactId>appengine-maven-plugin</artifactId>
-		<version>1.3.0</version>
 		<configuration>
 			<project>myproject</project>
 		</configuration>

spring-boot-project/spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -177,7 +177,6 @@ You also need to include the following element inside `<plugins/>`:
 	<plugin>
 		<groupId>org.apache.maven.plugins</groupId>
 		<artifactId>maven-resources-plugin</artifactId>
-		<version>2.7</version>
 		<configuration>
 			<delimiters>
 				<delimiter>@</delimiter>
@@ -2460,7 +2459,6 @@ To generate build information with Maven, add an execution for the `build-info`
 			<plugin>
 				<groupId>org.springframework.boot</groupId>
 				<artifactId>spring-boot-maven-plugin</artifactId>
-				<version>{spring-boot-version}</version>
 				<executions>
 					<execution>
 						<goals>
@@ -2572,7 +2570,6 @@ However, you must additionally add an `<executions>` section, as follows:
 			<plugin>
 				<groupId>org.springframework.boot</groupId>
 				<artifactId>spring-boot-maven-plugin</artifactId>
-				<version>{spring-boot-version}</version>
 				<executions>
 					<execution>
 						<goals>

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

@@ -120,7 +120,7 @@ For instance, to upgrade to another Spring Data release train, you could add the
 			<dependency>
 				<groupId>org.springframework.data</groupId>
 				<artifactId>spring-data-releasetrain</artifactId>
-				<version>Fowler-SR2</version>
+				<version>Moore-SR10</version>
 				<type>pom</type>
 				<scope>import</scope>
 			</dependency>