Remove deprecated StandardRequestHandler (#4135)

Co-authored-by: David Smiley <dsmiley@apache.org>

Author: epugh

changelog/unreleased/SOLR-18105.yml

@@ -0,0 +1,8 @@
+# See https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc
+title: Remove deprecated StandardRequestHandler in favor of SearchHandler
+type: removed # added, changed, fixed, deprecated, removed, dependency_update, security, other
+authors:
+  - name: Eric Pugh
+links:
+  - name: SOLR-18105
+    url: https://issues.apache.org/jira/browse/SOLR-18105

solr/core/src/java/org/apache/solr/handler/StandardRequestHandler.java

@@ -25,7 +25,7 @@
 
   <xi:include href="solrconfig.snippet.randomindexconfig.xml" xmlns:xi="http://www.w3.org/2001/XInclude"/>
 
-  <requestHandler name="standard" class="solr.StandardRequestHandler"/>
+  <requestHandler name="standard" class="solr.SearchHandler"/>
   <requestHandler name="/update" class="solr.UpdateRequestHandler"  />
 
   <valueSourceParser name="sin1" class="solr.ExpressionValueSourceParser">