Remove testing support from the CLI

The testing support in the CLI has proven to be more trouble than
it's worth. Our recommendation is that, once an app gets to the stage
of requiring a test suite, it should be converted to a Maven or
Gradle project. This makes it easy to version, publish, deploy etc
using the vast ecosystems of the two build systems.

As part of this change, the dependency management for Spock has been
moved into spring-boot-parent, thereby making it "private". This
allows it to continue to manage the test-only Spock dependency in
spring-boot-test without also managing the version of Spring that is
used by a user's application.

Closes gh-9087
Fixes gh-9043

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

@@ -252,41 +252,6 @@ http://platform.spring.io/[Spring IO Platform], e.g.
 
 
 
-[[cli-testing]]
-=== Testing your code
-The `test` command allows you to compile and run tests for your application. Typical
-usage looks like this:
-
-[indent=0]
-----
-	$ spring test app.groovy tests.groovy
-	Total: 1, Success: 1, : Failures: 0
-	Passed? true
-----
-
-In this example, `tests.groovy` contains JUnit `@Test` methods or Spock `Specification`
-classes. All the common framework annotations and static methods should be available to
-you without having to `import` them.
-
-Here is the `tests.groovy` file that we used above (with a JUnit test):
-
-[source,groovy,indent=0]
-----
-	class ApplicationTests {
-
-		@Test
-		void homeSaysHello() {
-			assertEquals("Hello World!", new WebApplication().home())
-		}
-
-	}
-----
-
-TIP: If you have more than one test source files, you might prefer to organize them
-into a `test` directory.
-
-
-
 [[cli-multiple-source-files]]
 === Applications with multiple source files
 You can use "`shell globbing`" with all commands that accept file input. This allows you
@@ -297,14 +262,6 @@ to easily use multiple files from a single directory, e.g.
 	$ spring run *.groovy
 ----
 
-This technique can also be useful if you want to segregate your "`test`" or "`spec`" code
-from the main application code:
-
-[indent=0]
-----
-	$ spring test app/*.groovy test/*.groovy
-----
-
 
 
 [[cli-jar]]