[CrOS Bluetooth] Use Disconnect in BluetoothDeviceClientImpl.

This change updates the implementation to use the previous disconnect
mechanism when not running on ChromeOS. This fixes an issue where
non-ChromeOS builds try to invoke the "DisconnectOld" method which does
not exist in upstream BlueZ.

Bug: 1332640
Test: 
Change-Id: I466ce0623fe1f9ed372b0c1b011eb8f1d9867be3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3690211
Commit-Queue: Chad Duffin <chadduffin@chromium.org>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1012219}

device/bluetooth/dbus/bluetooth_device_client.cc

@@ -28,9 +28,11 @@ namespace bluez {
 
 namespace {
 
+#if BUILDFLAG(IS_CHROMEOS_ASH)
 // TODO(b/213229904): Remove this constant and replace with
 // |bluetooth_device::kDisconnectOld| once it has been uprev'd.
 constexpr char kDisconnectOldPlaceholder[] = "DisconnectOld";
+#endif  // BUILDFLAG(IS_CHROMEOS_ASH)
 
 // Value returned for the the RSSI or TX power if it cannot be read.
 const int kUnknownPower = 127;
@@ -377,7 +379,7 @@ class BluetoothDeviceClientImpl : public BluetoothDeviceClient,
                                   ? bluetooth_device::kDisconnect
                                   : kDisconnectOldPlaceholder;
 #else   // BUILDFLAG(IS_CHROMEOS_ASH)
-    const char* method_name = kDisconnectOldPlaceholder;
+    const char* method_name = bluetooth_device::kDisconnect;
 #endif  // BUILDFLAG(IS_CHROMEOS_ASH)
     dbus::MethodCall method_call(bluetooth_device::kBluetoothDeviceInterface,
                                  method_name);