treewide: Reduce use of cstr! macro in favor of c"" literals

Cargo.toml

@@ -28,6 +28,8 @@ mutex-trait = "0.2"
 
 bare-metal = "1"
 
+# Only used for shell, where a macro is described to take a string literal and
+# in the macro implementation turns it into a CStr.
 cstr = "^0.2.11"
 
 heapless = "^0.8"

src/gcoap.rs

@@ -155,7 +155,7 @@ where
     /// [coap_handler::Handler], you can wrap it in [crate::coap_handler::GcoapHandler] to for adaptation.
     pub fn new_catch_all(handler: &'a mut H) -> Self {
         Self::new(
-            cstr::cstr!("/"),
+            c"/",
             riot_sys::COAP_GET
                 | riot_sys::COAP_POST
                 | riot_sys::COAP_PUT

src/panic.rs

@@ -22,7 +22,7 @@ fn panic(info: &::core::panic::PanicInfo) -> ! {
         unsafe {
             riot_sys::core_panic(
                 riot_sys::core_panic_t_PANIC_GENERAL_ERROR,
-                cstr::cstr!("RUST PANIC").as_ptr() as _,
+                c"RUST PANIC".as_ptr() as _,
             )
         };
     } else {