docs(README): remove outdated test concurrency workaround

Author: PiDelport

README.md

@@ -28,23 +28,3 @@ Helper script:
 ```shell
 ./runtests.sh
 ```
-
-Currently, some tests with static mocks can intermittently fail due to test thread concurrency.
-(For example, see test `rtc_enclave::tests::dcap_azure_attestation_works`.)
-
-To avoid this, run:
-
-```shell
-cargo test -- --test-threads=1
-```
-
-or set:
-
-```shell
-export RUST_TEST_THREADS=1
-```
-
-TODO(Pi): We should probably configure single-threading by default in affected crates
-once `cargo test` implements this:
-
-* [Enable specifying --test-threads in Cargo.toml #8430](https://github.com/rust-lang/cargo/issues/8430)