Migrate from AndroidManifest to build.gradle for namespace

AGP has deprecated use of packageName in AndroidManifest and
instead wants everyone to use `android { namespace = "foo" }`
in build.gradle files.

Test: ./gradlew tasks -> still passes
Change-Id: I647d9abecfac44747b351f020904c3e43f2cbc87
diff --git a/docs-public/build.gradle b/docs-public/build.gradle
index d0f6958..f43fd20 100644
--- a/docs-public/build.gradle
+++ b/docs-public/build.gradle
@@ -3,6 +3,10 @@
     id("AndroidXDocsPlugin")
 }
 
+android {
+    namespace "androidx.docs.publicdocs"
+}
+
 dependencies {
     docs("androidx.activity:activity:1.5.0")
     docs("androidx.activity:activity-compose:1.5.0")
diff --git a/docs-public/src/main/AndroidManifest.xml b/docs-public/src/main/AndroidManifest.xml
deleted file mode 100644
index c0c456b..0000000
--- a/docs-public/src/main/AndroidManifest.xml
+++ /dev/null
@@ -1,16 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?><!--
-  ~ Copyright 2020 The Android Open Source Project
-  ~
-  ~ Licensed under the Apache License, Version 2.0 (the "License");
-  ~ you may not use this file except in compliance with the License.
-  ~ You may obtain a copy of the License at
-  ~
-  ~      http://www.apache.org/licenses/LICENSE-2.0
-  ~
-  ~ Unless required by applicable law or agreed to in writing, software
-  ~ distributed under the License is distributed on an "AS IS" BASIS,
-  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-  ~ See the License for the specific language governing permissions and
-  ~ limitations under the License.
-  -->
-<manifest package="androidx.docs.publicdocs"/>