init: Refactor selinux.h/cpp

This change factors out functions that handle selabels from
selinux.h/cpp into selabel.h/cpp.  This allows util.cpp to be used by
the upcoming native zygote without a bunch of define flags that are
required for selinux.cpp.

Bug: 133443795
Test: Build and boot cuttlefish.
Change-Id: Ie238a96c6407c6698a605dd8803c1727abfaae7b
diff --git a/init/selinux.h b/init/selinux.h
index c7d6647..63ad470 100644
--- a/init/selinux.h
+++ b/init/selinux.h
@@ -14,11 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _INIT_SELINUX_H
-#define _INIT_SELINUX_H
-
-#include <string>
-#include <vector>
+#pragma once
 
 namespace android {
 namespace init {
@@ -29,15 +25,7 @@
 void SelinuxSetupKernelLogging();
 int SelinuxGetVendorAndroidVersion();
 
-void SelabelInitialize();
-bool SelabelLookupFileContext(const std::string& key, int type, std::string* result);
-bool SelabelLookupFileContextBestMatch(const std::string& key,
-                                       const std::vector<std::string>& aliases, int type,
-                                       std::string* result);
-
 static constexpr char kEnvSelinuxStartedAt[] = "SELINUX_STARTED_AT";
 
 }  // namespace init
 }  // namespace android
-
-#endif