remove depenency on cortex-m

Author: jannic

firmware/defmt-rtt/Cargo.toml

@@ -11,6 +11,5 @@ repository = "https://github.com/knurling-rs/defmt"
 version = "0.3.0"
 
 [dependencies]
-cortex-m = "0.7"
 defmt = { version = "0.3", path = "../../defmt" }
 critical-section = "0.2.5"