Remove removed argument from docs

Author: oli-obk

miri

@@ -15,9 +15,6 @@ Just build miri. <flags> are passed to `cargo build`.
 ./miri check <flags>:
 Just check miri. <flags> are passed to `cargo check`.
 
-./miri cargo <flags>:
-Run `cargo miri <flags>`.
-
 ./miri test <flags>:
 Build miri, set up a sysroot and then run the test suite. <flags> are passed
 to the final `cargo test` invocation.