examples Remove the fn config() idiom.

It was only useful for doing #[embassy_executor::main(config = "config()")]`. Now that
it's gone, it makes more sense to build the config in main directly.

examples/stm32h7/src/bin/adc.rs

@@ -11,18 +11,15 @@ use embassy_stm32::time::mhz;
 use embassy_stm32::Config;
 use {defmt_rtt as _, panic_probe as _};
 
-pub fn config() -> Config {
+#[embassy_executor::main]
+async fn main(_spawner: Spawner) {
     let mut config = Config::default();
     config.rcc.sys_ck = Some(mhz(400));
     config.rcc.hclk = Some(mhz(200));
     config.rcc.per_ck = Some(mhz(64));
     config.rcc.adc_clock_source = AdcClockSource::PerCk;
-    config
-}
+    let mut p = embassy_stm32::init(config);
 
-#[embassy_executor::main]
-async fn main(_spawner: Spawner) {
-    let mut p = embassy_stm32::init(config());
     info!("Hello World!");
 
     let mut adc = Adc::new(p.ADC3, &mut Delay);