Allow package prefix in docs (#5736)

Per [b/326624050](https://b.corp.google.com/issues/326624050),

This deletes the configuration that was removing the package prefix from
our toc files.

We previously needed to remove the `com.google` package prefix from our
docs; since of the SDKs were still using the old doc engine. Now that
everyone has migrated, this is no longer needed. We should remove this
transformation from our doc generation to align with internal systems.

buildSrc/src/main/java/com/google/firebase/gradle/plugins/DackkaGenerationTask.kt

@@ -153,7 +153,6 @@ constructor(private val workerExecutor: WorkerExecutor) : GenerateDocumentationT
                       "docRootPath" to "/docs/reference/",
                       "javaDocsPath" to "android",
                       "kotlinDocsPath" to "kotlin",
-                      "packagePrefixToRemoveInToc" to "com.google",
                       "projectPath" to "client/${clientName.get()}",
                       "includedHeadTagsPathJava" to
                         "docs/reference/android/_reference-head-tags.html",