stm32: remove subghz feature.

It's available only on WL. if you're using a WL, you want subghz for sure.

embassy-stm32/src/lib.rs

@@ -53,6 +53,8 @@ pub mod rng;
 pub mod sdmmc;
 #[cfg(spi)]
 pub mod spi;
+#[cfg(stm32wl)]
+pub mod subghz;
 #[cfg(usart)]
 pub mod usart;
 #[cfg(all(usb, feature = "time"))]
@@ -62,9 +64,6 @@ pub mod usb_otg;
 #[cfg(iwdg)]
 pub mod wdg;
 
-#[cfg(feature = "subghz")]
-pub mod subghz;
-
 // This must go last, so that it sees all the impl_foo! macros defined earlier.
 pub(crate) mod _generated {
     #![allow(dead_code)]