SpringBoot Simplify build.gradle for spring-boot-starter-data-solr

It currently declares four dependencies:

1. org.springframework.boot:spring-boot-starter
2. org.apache.httpcomponents
3. org.apache.solr:solrj
4. org.springframework.data:spring-data-solr

2 and 3 are transitive dependencies of 4, so we can simplify things by just declaring a dependency on org.springframework.data:spring-data-solr with the exclusions that are currently declared in 2 and 3.