[build] Clean up Gradle configs (#5685)

Putting an early exit if statement at the top instead of wrapping the
whole file contents unbreaks unit test configs, as was discovered for
SysId. It reduces nesting as well.

Unused plugins were removed from the beginnings of files as well.

simulation/halsim_ws_server/build.gradle

@@ -1,3 +1,6 @@
+if (project.hasProperty('onlylinuxathena')) {
+    return;
+}
 
 description = "WebSocket Server Extension"
 
@@ -20,25 +23,20 @@ apply from: "${rootDir}/shared/plugins/setupBuild.gradle"
 
 model {
     testSuites {
-        def comps = $.components
-        if (!project.hasProperty('onlylinuxathena')) {
-            "${pluginName}Test"(GoogleTestTestSuiteSpec) {
-                for(NativeComponentSpec c : comps) {
-                    if (c.name == pluginName) {
-                        testing c
-                        break
-                    }
+        "${pluginName}Test"(GoogleTestTestSuiteSpec) {
+            for(NativeComponentSpec c : $.components) {
+                if (c.name == pluginName) {
+                    testing c
+                    break
                 }
-                sources {
-                    cpp {
-                        source {
-                            srcDirs 'src/test/native/cpp'
-                            include '**/*.cpp'
-                        }
-                        exportedHeaders {
-                            srcDirs 'src/test/native/include', 'src/main/native/cpp'
-                        }
-                    }
+            }
+            sources.cpp {
+                source {
+                    srcDirs 'src/test/native/cpp'
+                    include '**/*.cpp'
+                }
+                exportedHeaders {
+                    srcDirs 'src/test/native/include', 'src/main/native/cpp'
                 }
             }
         }