Remove redundant Quartz exclusion

Quartz is an optional dependency of spring-context-support so there's
no need to exclude it

This is a baby-step towards using the Spring Framework bom (#955)

spring-boot-dependencies/pom.xml

@@ -821,12 +821,6 @@
 				<groupId>org.springframework</groupId>
 				<artifactId>spring-context-support</artifactId>
 				<version>${spring.version}</version>
-				<exclusions>
-					<exclusion>
-						<groupId>quartz</groupId>
-						<artifactId>quartz</artifactId>
-					</exclusion>
-				</exclusions>
 			</dependency>
 			<dependency>
 				<groupId>org.springframework</groupId>