Revert "Use cp instead of install for ndk_headers"

This reverts commit 1202729cb215ea039306a2e2b88eddaff20b73cd.

Reason for revert: Breaks aosp-main/ndk builds

Change-Id: I453792f7f974dc336d5f6775adfc5899b8d34d7b
diff --git a/cc/ndk_sysroot.go b/cc/ndk_sysroot.go
index e815172..483d23b 100644
--- a/cc/ndk_sysroot.go
+++ b/cc/ndk_sysroot.go
@@ -69,12 +69,12 @@
 	ctx.RegisterParallelSingletonType("ndk", NdkSingleton)
 }
 
-func getNdkInstallBase(ctx android.PathContext) android.OutputPath {
+func getNdkInstallBase(ctx android.PathContext) android.InstallPath {
 	return android.PathForNdkInstall(ctx)
 }
 
 // Returns the main install directory for the NDK sysroot. Usable with --sysroot.
-func getNdkSysrootBase(ctx android.PathContext) android.OutputPath {
+func getNdkSysrootBase(ctx android.PathContext) android.InstallPath {
 	return getNdkInstallBase(ctx).Join(ctx, "sysroot")
 }