[pvmfw][microdroid] Make empty_file filegroup for reuse

Test: m pvmfw_test microdroid_initrd_debuggable \
 microdroid_initrd_normal
Change-Id: I9767ee97900e1b9fa60c45eee8556012cb9e0c20
diff --git a/microdroid/initrd/Android.bp b/microdroid/initrd/Android.bp
index ff6314b..22a06e1 100644
--- a/microdroid/initrd/Android.bp
+++ b/microdroid/initrd/Android.bp
@@ -107,7 +107,7 @@
 prebuilt_etc {
     name: "microdroid_initrd_debuggable",
     // We don't have ramdisk for architectures other than x86_64 & arm64
-    src: "empty_file",
+    src: ":empty_file",
     arch: {
         x86_64: {
             src: ":microdroid_initrd_debuggable_x86_64",
@@ -122,7 +122,7 @@
 prebuilt_etc {
     name: "microdroid_initrd_normal",
     // We don't have ramdisk for architectures other than x86_64 & arm64
-    src: "empty_file",
+    src: ":empty_file",
     arch: {
         x86_64: {
             src: ":microdroid_initrd_normal_x86_64",
diff --git a/microdroid/initrd/empty_file b/microdroid/initrd/empty_file
deleted file mode 100644
index e69de29..0000000
--- a/microdroid/initrd/empty_file
+++ /dev/null