installd: add command 'removeIdmap'

Add an installd command to remove an idmap file. This is the inverse of
the 'idmap' command and is intended for clean-up once an idmap file is
no longer needed because an APK was removed, etc.

This commit depends on a corresponding commit in frameworks/base (with
the same Change-Id).

Bug: 31052947
Test: run tests from 'OMS: tests for OverlayManagerService'
Change-Id: Iae19a519803f0c172b02a32faa283ef36f43863c
diff --git a/cmds/installd/InstalldNativeService.h b/cmds/installd/InstalldNativeService.h
index 0a9f12f..c8b5927 100644
--- a/cmds/installd/InstalldNativeService.h
+++ b/cmds/installd/InstalldNativeService.h
@@ -92,6 +92,7 @@
 
     binder::Status idmap(const std::string& targetApkPath, const std::string& overlayApkPath,
             int32_t uid);
+    binder::Status removeIdmap(const std::string& overlayApkPath);
     binder::Status rmPackageDir(const std::string& packageDir);
     binder::Status markBootComplete(const std::string& instructionSet);
     binder::Status freeCache(const std::unique_ptr<std::string>& uuid, int64_t freeStorageSize,