DO NOT MERGE: Fix ActivityManager#killBackgroundProcesses permissions

In the pevious CL, we incorrectly added the permission check in the
killBackgroundProcessesExcept. Now fix this issue.

Bug: 239423414
Bug: 223376078
Test: atest CtsAppTestCases:ActivityManagerTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:9a14267036edef6224a7418f92b9d3f88f2ac5b7)
Merged-In: I9471a77188ee63ec32cd0c81569193e4ccad885b
Change-Id: I9471a77188ee63ec32cd0c81569193e4ccad885b

services/core/java/com/android/server/am/ActivityManagerService.java

diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index 2f74f3b..b106677 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -3745,22 +3745,6 @@
             throw new SecurityException(msg);
         }
 
-        final int callingUid = Binder.getCallingUid();
-        final int callingPid = Binder.getCallingPid();
-
-        ProcessRecord proc;
-        synchronized (mPidsSelfLocked) {
-            proc = mPidsSelfLocked.get(callingPid);
-        }
-        if (callingUid >= FIRST_APPLICATION_UID
-                && (proc == null || !proc.info.isSystemApp())) {
-            final String msg = "Permission Denial: killAllBackgroundProcesses() from pid="
-                    + callingPid + ", uid=" + callingUid + " is not allowed";
-            Slog.w(TAG, msg);
-            // Silently return to avoid existing apps from crashing.
-            return;
-        }
-
         final long callingId = Binder.clearCallingIdentity();
         try {
             synchronized (this) {