Revert "Relocate 'api_identity' derive macro - it's a helper for omicron-common (#288)"

This reverts commit ec737d3.

Author: david-crespo

common/src/api/external/api_identity/.gitignore renamed to api_identity/.gitignore

@@ -43,8 +43,8 @@ fn do_object_identity(item: TokenStream) -> Result<TokenStream, syn::Error> {
     };
 
     let stream = quote! {
-        impl crate::api::external::ObjectIdentity for #name {
-            fn identity(&self) -> &crate::api::external::IdentityMetadata {
+        impl ObjectIdentity for #name {
+            fn identity(&self) -> &IdentityMetadata {
                 &self.identity
             }
         }
@@ -68,8 +68,8 @@ mod test {
         );
 
         let expected = quote! {
-            impl crate::api::external::ObjectIdentity for Foo {
-                fn identity(&self) -> &crate::api::external::IdentityMetadata {
+            impl ObjectIdentity for Foo {
+                fn identity(&self) -> &IdentityMetadata {
                     &self.identity
                 }
             }

common/src/api/external/api_identity/Cargo.toml renamed to api_identity/Cargo.toml

@@ -27,7 +27,7 @@ progenitor = { git = "https://github.com/oxidecomputer/progenitor" }
 percent-encoding = "2.1.0"
 
 [dependencies.api_identity]
-path = "src/api/external/api_identity"
+path = "../api_identity"
 
 [dependencies.backoff]
 version = "0.3.0"