macros: remove embassy_prefix attr.

This was used in the past for reexporting the macros from drogue-device,
which is no longer using it.

Also, it is a pain to support, so we don't want it.

embassy-macros/src/util/mod.rs

@@ -1,2 +1 @@
 pub mod ctxt;
-pub mod path;

embassy-macros/src/util/path.rs

@@ -1,41 +0,0 @@
-use darling::{FromMeta, Result};
-use proc_macro2::Span;
-use syn::{LitStr, Path};
-
-#[derive(Debug)]
-pub struct ModulePrefix {
-    literal: LitStr,
-}
-
-impl ModulePrefix {
-    pub fn new(path: &str) -> Self {
-        let literal = LitStr::new(path, Span::call_site());
-        Self { literal }
-    }
-
-    pub fn append(&self, component: &str) -> ModulePrefix {
-        let mut lit = self.literal().value();
-        lit.push_str(component);
-        Self::new(lit.as_str())
-    }
-
-    pub fn path(&self) -> Path {
-        self.literal.parse().unwrap()
-    }
-
-    pub fn literal(&self) -> &LitStr {
-        &self.literal
-    }
-}
-
-impl FromMeta for ModulePrefix {
-    fn from_string(value: &str) -> Result<Self> {
-        Ok(ModulePrefix::new(value))
-    }
-}
-
-impl Default for ModulePrefix {
-    fn default() -> ModulePrefix {
-        ModulePrefix::new("::")
-    }
-}