Remove the LOC of the expected failure

This exact line where the assertion is may change whenever we update the
rust toolchain, which makes this test unreliable. We still ensure that
the assertion fails. Note that this may still fail if the message or the
check gets updated, but this shouldn't happen frequently.

Author: celinval

rmc-docs/src/tutorial/arbitrary-variables/unsafe_update.expected

@@ -1,3 +1,3 @@
 [inventory::verification::unsafe_update.assertion.1] line 61 assertion failed: inventory.get(&id).unwrap() == quantity: SUCCESS
-[std::option::Option::<T>::unwrap.assertion.1] line 759 called `Option::unwrap()` on a `None` value: FAILURE
+called `Option::unwrap()` on a `None` value: FAILURE
 VERIFICATION FAILED