rust: Don't force toolchain for examples

Author: chrysn

examples/rust-gcoap/Makefile

@@ -41,8 +41,6 @@ BASELIBS += $(APPLICATION_RUST_MODULE).module
 
 FEATURES_REQUIRED += rust_target
 
-CARGO_CHANNEL ?= stable
-
 # Currently unknown, something related to the LED_PORT definition that doesn't
 # pass C2Rust's transpilation
 BOARD_BLACKLIST := ek-lm4f120xl

examples/rust-hello-world/Makefile

@@ -21,11 +21,6 @@ BASELIBS += $(APPLICATION_RUST_MODULE).module
 
 FEATURES_REQUIRED += rust_target
 
-# All Rust components RIOT uses work on stable Rust. If any extra libraries
-# were to require a more recent version, switch to `CARGO_CHANNEL =
-# $(CARGO_CHANNEL_NIGHTLY)` to use whichever nightly version is available.
-CARGO_CHANNEL ?= stable
-
 # Currently unknown, something related to the LED_PORT definition that doesn't
 # pass C2Rust's transpilation
 BOARD_BLACKLIST := ek-lm4f120xl