ToolsInstaller: do not use R

This is horible! But ToolsInstaller uses lots of other error strings
nakedly, as does ModuleLoader. These both need to be fixed up the proper
way (like the last two commits). This commit here is just to make the
initial porting a bit easier.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/util/ToolsInstaller.java

@@ -12,7 +12,6 @@ import android.util.Log;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.BuildConfig;
-import com.wireguard.android.R;
 import com.wireguard.android.util.RootShell.RootShellException;
 
 import java.io.File;
@@ -101,8 +100,7 @@ public final class ToolsInstaller {
                 }
             }
             if (!areToolsAvailable)
-                throw new FileNotFoundException(
-                        context.getString(R.string.tools_unavailable_error));
+                throw new FileNotFoundException("Required tools unavailable");
         }
     }