build: revert skip-shading for gapic-generator-java

Keep gapic-generator-java shaded so its executable protoc plugin binary remains functional.

Author: lqiu96

sdk-platform-java/gapic-generator-java-pom-parent/pom.xml

@@ -45,9 +45,6 @@
     <!--  skipping clirr check for protobuf 4.x upgrade -->
     <clirr.skip>true</clirr.skip>
     <ignoreNonCompile>true</ignoreNonCompile><!-- maven-dependency-plugin:analyze to skip test scope dependencies -->
-    <!-- maven-shade-plugin does not define a built-in user property for its skip parameter;
-         shade.skip is declared here and mapped in shaded modules to allow quick-build to toggle it off. -->
-    <shade.skip>false</shade.skip>
   </properties>
 
   <developers>
@@ -98,7 +95,6 @@
         <fmt.skip>true</fmt.skip>
         <flatten.skip>true</flatten.skip>
         <mdep.analyze.skip>true</mdep.analyze.skip>
-        <shade.skip>true</shade.skip>
       </properties>
     </profile>
 

sdk-platform-java/gapic-generator-java/pom.xml

@@ -255,7 +255,6 @@
               <goal>shade</goal>
             </goals>
             <configuration>
-              <skip>${shade.skip}</skip>
               <createDependencyReducedPom>false</createDependencyReducedPom>
               <filters>
                 <filter>