tock-register-interface: remove std_unit_tests feature

With no tests relying on the standard library being generated, the
feature for explicitly enabling the generation of these tests can be
removed.

Author: lschuermann

libraries/tock-register-interface/Cargo.toml

@@ -15,14 +15,9 @@ edition = "2021"
 travis-ci = { repository = "tock/tock", branch = "master" }
 
 [features]
-default = [ "register_types", "std_unit_tests" ]
+default = [ "register_types" ]
 
 # Include actual register types (except LocalRegisterCopy). Disabling
 # the feature makes this an interface-only library and removes all
 # usage of unsafe code
 register_types = []
-
-# Feature flag to enable generation of unit tests for the
-# registers. Enabling this may break compilation in
-# `custom-test-frameworks` environments.
-std_unit_tests = []

libraries/tock-register-interface/README.md

@@ -90,22 +90,16 @@ struct Registers {
 }
 ```
 
-By default, `std` unit tests for the struct are generated as well (that is,
-tests attributed with `#[test]`). The unit tests make sure that the offsets and
-padding are consistent with the actual fields in the struct, and that alignment
-is correct.
-
-Since those tests would break compilation in `custom-test-frameworks`
-environments, it is possible to opt out of the test generation. To do
-so, disable the default feature set containing the `std_unit_tests`
-feature:
-
-```toml
-[dependencies.tock-registers]
-version = "0.4.x"
-default-features = false
-features = ["register_types"]
-```
+This crate will generate additional, compile time (`const`) assertions
+to validate various invariants of the register structs, such as
+
+- proper start offset of padding fields,
+- proper start and end offsets of actual fields,
+- invalid alignment of field types,
+- the `@END` marker matching the size of the struct.
+
+For more information on the generated assertions, check out the [`test_fields!`
+macro documentation](https://docs.tockos.org/tock_registers/macro.test_fields.html).
 
 By default, the visibility of the generated structs and fields is private. You
 can make them public using the `pub` keyword, just before the struct name or the