init selinux.cpp: use a better way to detect if we run in Microdroid

We are now conditionally compiling init binaries & libinit for
Microdroid (adding -DMICRODROID=1 cflag), so instead of checking for the
presence of the /system/etc/selinux/microdroid_precompiled_sepolicy we
can check if the code is compiled for Microdroid.

In a follow-up changes we can split the sepolicy loading logic into 2
separate headers (one for Android and one for Microdroid) and include
the necessary one depending on the target we compile for.

Bug: 287206497
Test: atest MicrodroidTestApp
Change-Id: Id9c837d03a96ff9564688d33955ec85094eee487
diff --git a/init/fuzzer/Android.bp b/init/fuzzer/Android.bp
index c21a196..856ca8c 100644
--- a/init/fuzzer/Android.bp
+++ b/init/fuzzer/Android.bp
@@ -18,7 +18,7 @@
 }
 
 cc_defaults {
-    name: "libinit_defaults",
+    name: "libinit_fuzzer_defaults",
     static_libs: [
         "libc++fs",
         "liblmkd_utils",
@@ -53,7 +53,7 @@
     ],
     shared_libs: ["libhidlmetadata",],
     defaults: [
-        "libinit_defaults",
+        "libinit_fuzzer_defaults",
     ],
 }
 
@@ -62,7 +62,7 @@
     srcs: [
         "init_property_fuzzer.cpp",
     ],
-    defaults: ["libinit_defaults"],
+    defaults: ["libinit_fuzzer_defaults"],
 }
 
 cc_fuzz {
@@ -71,6 +71,6 @@
         "init_ueventHandler_fuzzer.cpp",
     ],
     defaults: [
-        "libinit_defaults",
+        "libinit_fuzzer_defaults",
     ],
 }