rustdoc: remove link to doc/compiler.md

I'm not sure if it's possible to link to .md files in the source code.
If so, this isn't the way to do it.

Author: apoelstra

src/policy/concrete.rs

@@ -346,7 +346,7 @@ impl<Pk: MiniscriptKey> Policy<Pk> {
     ///
     /// It is **not recommended** to use policy as a stable identifier for a miniscript. You should
     /// use the policy compiler once, and then use the miniscript output as a stable identifier. See
-    /// the compiler document in [`doc/compiler.md`] for more details.
+    /// the compiler document in `doc/compiler.md` for more details.
     #[cfg(feature = "compiler")]
     pub fn compile_to_descriptor<Ctx: ScriptContext>(
         &self,
@@ -375,7 +375,7 @@ impl<Pk: MiniscriptKey> Policy<Pk> {
     ///
     /// It is **not recommended** to use policy as a stable identifier for a miniscript. You should
     /// use the policy compiler once, and then use the miniscript output as a stable identifier. See
-    /// the compiler document in doc/compiler.md for more details.
+    /// the compiler document in `doc/compiler.md` for more details.
     #[cfg(feature = "compiler")]
     pub fn compile<Ctx: ScriptContext>(&self) -> Result<Miniscript<Pk, Ctx>, CompilerError> {
         self.is_valid()?;