fix(example/ch32v208): remove defmt feature

This patch removes the defmt feature from ch32-hal in the example.
- Using defmt requires that special linker script setup, and it is not
present
- I also don't believe that these simple examples should depend on defmt
anyways, especially that we can't do defmt over rtt currently.

examples/ch32v208/Cargo.toml

@@ -6,7 +6,6 @@ edition = "2021"
 [dependencies]
 ch32-hal = { path = "../../", features = [
     "ch32v208wbu6",
-    "defmt",
     "embassy",
     "rt",
 ], default-features = false }