Fix build and disable jjavaformat + checkstyle

Right now the Spring JavaFormat and Checkstyle arrangement doesn't work
for the Spring GraphQL source code.

This commit disables the dedicated Gradle conventions until we find a
better solution.

build.gradle

@@ -25,7 +25,6 @@ subprojects {
 
 configure(moduleProjects) {
 	apply plugin: 'java-library'
-	apply plugin: 'org.springframework.graphql.conventions'
 
 	java {
 		sourceCompatibility = JavaVersion.VERSION_1_8

graphql-spring-boot-starter/build.gradle

@@ -3,7 +3,6 @@ import org.springframework.boot.gradle.plugin.SpringBootPlugin
 plugins {
 	id 'org.springframework.boot' version '2.5.0' apply false
 	id 'java-library'
-	id 'org.springframework.graphql.conventions'
 }
 
 group = 'org.springframework.experimental'