Remove downgrade check for targetSandboxLevel

This is causing issues with apps adopting Instant Apps and the security
requirements that lead to downgrade being disallowed were either
reverted in late O or moved into target API checks.

Change-Id: Ide3913091788d6a37bf2d17ca22769f6bbc6d3c7
Fixes: 80307033
Test: Install v2 sandbox APK, try and upgrade with a v1 sandbox APK.

services/core/java/com/android/server/pm/PackageManagerService.java

@@ -17260,17 +17260,6 @@ public class PackageManagerService extends IPackageManager.Stub
                                         + "Persistent apps are not updateable.");
                         return;
                     }
-                    // Prevent apps from downgrading their targetSandbox.
-                    final int oldTargetSandbox = oldPackage.applicationInfo.targetSandboxVersion;
-                    final int newTargetSandbox = pkg.applicationInfo.targetSandboxVersion;
-                    if (oldTargetSandbox == 2 && newTargetSandbox != 2) {
-                        res.setError(PackageManager.INSTALL_FAILED_SANDBOX_VERSION_DOWNGRADE,
-                                "Package " + pkg.packageName + " new target sandbox "
-                                + newTargetSandbox + " is incompatible with the previous value of"
-                                + oldTargetSandbox + ".");
-                        return;
-                    }
-
                     // Prevent installing of child packages
                     if (oldPackage.parentPackage != null) {
                         res.setError(PackageManager.INSTALL_PARSE_FAILED_BAD_PACKAGE_NAME,