Stop signing the war file with jarsigner (#26708)

* Stop signing the war file with jarsigner

The Jenkins code signing certificate that was issued by Digicert in 2023
will expire May 16, 2026.  The replacement code signing process is able
to sign MSI installer files, but is not able to sign war files and other
Java objects.

The Jenkins war file will continue to be signed with the GPG private key
of the Jenkins project.  Detailed instructions to verify the signing
of the Jenkins war file are included in the Jenkins documentaiton at
https://www.jenkins.io/download/verify/

A SHA-256 checksum is also provided for the Jenkins war file to further
assure there has been no data corruption or tampering with the contents
of the war file.

https://github.com/jenkins-infra/helpdesk/issues/4923 is the Jenkins
infrastructure help desk ticket that tracks the update of the MSI code
signing process.

Testing done:

* Confirmed that compilation works as expected
* Confirmed that all tests continue to pass after this change

* Remove unreferenced dummy.keystore

pom.xml

@@ -175,21 +175,6 @@ THE SOFTWARE.
             </environmentVariables>
           </configuration>
         </plugin>
-        <plugin>
-          <artifactId>maven-jarsigner-plugin</artifactId>
-          <version>3.1.0</version>
-          <configuration>
-            <!--
-              during the development, debug profile will cause
-              the jars to be signed by a self-certified dummy public key.
-
-              For release, you should define the real values in ~/.m2/settings.xml
-            -->
-            <alias>${hudson.sign.alias}</alias>
-            <storepass>${hudson.sign.storepass}</storepass>
-            <keystore>${hudson.sign.keystore}</keystore>
-          </configuration>
-        </plugin>
         <plugin>
           <groupId>org.kohsuke</groupId>
           <artifactId>access-modifier-checker</artifactId>
@@ -392,11 +377,6 @@ THE SOFTWARE.
       <activation>
         <activeByDefault>true</activeByDefault>
       </activation>
-      <properties>
-        <hudson.sign.alias>jenkins</hudson.sign.alias>
-        <hudson.sign.keystore>../dummy.keystore</hudson.sign.keystore>
-        <hudson.sign.storepass>jenkins</hudson.sign.storepass>
-      </properties>
     </profile>
     <profile>
       <id>release</id>

war/pom.xml

@@ -762,35 +762,4 @@ THE SOFTWARE.
       </plugin>
     </plugins>
   </build>
-
-  <profiles>
-    <profile>
-      <!-- sign war -->
-      <id>sign</id>
-      <build>
-        <plugins>
-          <plugin>
-            <artifactId>maven-jarsigner-plugin</artifactId>
-            <executions>
-              <execution>
-                <id>signWar</id>
-                <goals>
-                  <goal>sign</goal>
-                </goals>
-                <phase>pre-integration-test</phase>
-                <configuration>
-                  <archive>${project.build.directory}/${project.build.finalName}.war</archive>
-                  <arguments>
-                    <argument>-tsa</argument>
-                    <argument>http://timestamp.digicert.com</argument>
-                  </arguments>
-                </configuration>
-              </execution>
-            </executions>
-          </plugin>
-        </plugins>
-      </build>
-    </profile>
-
-  </profiles>
 </project>