tools: Remove stale entry from .gitmodules

Signed-off-by: Samuel Holland <samuel@sholland.org>

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "app/tools/wireguard"]
 	path = app/tools/wireguard
 	url = https://git.zx2c4.com/WireGuard
-[submodule "app/tools/wireguard-android-integration"]
-	path = app/tools/wireguard-android-integration
-	url = https://git.zx2c4.com/android_kernel_wireguard