pom.xml: remove org.checkerframework:checker-qual

This was only pinned to avoid dependency convergence issues between
org.postgresql:postgresql and org.apache.solr:solr-core, but as of
version 42.7.11, org.postgresql:postgresql no longer depends on it.

Author: alanorth

pom.xml

@@ -1449,13 +1449,6 @@
                 <version>${asm.version}</version>
             </dependency>
 
-            <!-- Solr-core and Postgres disagree on versions of Checker Qual -->
-            <dependency>
-                <groupId>org.checkerframework</groupId>
-                <artifactId>checker-qual</artifactId>
-                <version>3.54.0</version>
-            </dependency>
-
             <!-- Several dependencies disagree on version of GSON including Jena, Google-OAuth-Client
                  and OpenAIRE Broker-Client -->
             <dependency>