[trusty] Remove unused FallibleVec import

After properly namespacing the dependencies of the service_dispatcher!
macro, there are some usused imports that should be removed

New Stuff:
* Removed an import of FallibleVec

Bug: 312749603

Change-Id: Iafc21762659ce0174a07d22c7fc256f7039a8bf6
Signed-off-by: Ross Kettleson <kettro@google.com>
diff --git a/ipc_manager.rs b/ipc_manager.rs
index e6db205..93881ff 100644
--- a/ipc_manager.rs
+++ b/ipc_manager.rs
@@ -40,7 +40,6 @@
     service_dispatcher, ConnectResult, Deserialize, Handle, Manager, MessageResult, PortCfg,
     Serialize, Serializer, Service, TipcError, Uuid,
-use trusty_std::alloc::FallibleVec;
 use trusty_std::alloc::TryAllocFrom;
 /// Port that handles new style keymint messages from non-secure world