SOLR-15263: Use 'remote' URLs for lucene javadocs in ref-guide

This allows us to re-enable the checkLocalJavadocLinksSite task, and in theory will point to the 'correct' URLs once 9.0 comes out, but there are longer term fixes still needed (see SOLR-15262)

build.gradle

@@ -191,7 +191,6 @@ apply from: file('gradle/hacks/gradle.gradle')
 apply from: file('gradle/hacks/hashmapAssertions.gradle')
 
 apply from: file('gradle/solr-tlp-migration/inaccessible-test-sources.gradle')
-apply from: file('gradle/solr-tlp-migration/disable-links-checking.gradle')
 
 apply from: file('gradle/solr/packaging.gradle') // SOLR ONLY
 apply from: file('gradle/solr/solr-forbidden-apis.gradle') // SOLR ONLY

solr/solr-ref-guide/build.gradle

@@ -121,6 +121,7 @@ ext {
  desc: 'HTML Site for publishing to the Solr website',
  props: [
  htmlSolrJavadocs: "https://lucene.apache.org/solr/${solrGuideVersionPath}_0/",
+ // TODO: This isn't viable long term - see SOLR-15262 / SOLR-15264
  htmlLuceneJavadocs: "https://lucene.apache.org/core/${solrGuideVersionPath}_0/"
  ]
  ]
@@ -132,8 +133,8 @@ ext {
  // NOTE: extra '../' because we'll in a sub-dir of buildDir that will be built later...
  props: [
  htmlSolrJavadocs : 'link:../' + buildDir.toPath().relativize(project(':solr:documentation').docroot.toPath()).toString().replace(File.separator, '/'),
- // TODO: decide what to do with lucene javadocs
- htmlLuceneJavadocs : 'link:../'
+ // TODO: This isn't viable long term - see SOLR-15262 / SOLR-15264
+ htmlLuceneJavadocs : "https://lucene.apache.org/core/${solrGuideVersionPath}_0/"
  ]
  ]
 }