Document rpi manifests and support multi-source remove_projects

Add header comment naming the AOSP release, and switch remove_projects
to a list so multiple remove-project XML fragments can be merged by
environ.py.

rpi/repo-shallow.yml

@@ -1,3 +1,4 @@
+# Android 17.0.0_r1 local manifest for PawletOS on Raspberry Pi
 repo:
   url: "https://android.googlesource.com/platform/manifest"
   branch: "android-17.0.0_r1"
@@ -8,7 +9,8 @@ repo:
     manifest_brcm_rpi: "https://git.oxmc.me/PawletOS/android_local_manifest/raw/branch/android-17.0/rpi/vendor/brcm_rpi.xml"
     manifest_lineageos: "https://git.oxmc.me/PawletOS/android_local_manifest/raw/branch/android-17.0/common/vendor/lineageos.xml"
     manifest_pawletos: "https://git.oxmc.me/PawletOS/android_local_manifest/raw/branch/android-17.0/rpi/pawletos.xml"
-    remove_projects: "https://git.oxmc.me/PawletOS/android_local_manifest/raw/branch/android-17.0/common/remove_projects.xml"
+    remove_projects:
+      - "https://git.oxmc.me/PawletOS/android_local_manifest/raw/branch/android-17.0/common/remove_projects.xml"
 
 patches:
   dirs:

rpi/repo.yml

@@ -1,3 +1,4 @@
+# Android 17.0.0_r1 local manifest for PawletOS on Raspberry Pi
 repo:
   url: "https://android.googlesource.com/platform/manifest"
   branch: "android-17.0.0_r1"