Remove proc-macro-nested crate.

It doesn't seem to be used anywhere.

Test: m rust
Change-Id: I45a21b036063625164515e0668e8f61a08a1b84b
diff --git a/default.xml b/default.xml
index b49b12c..e3dd770 100644
--- a/default.xml
+++ b/default.xml
@@ -707,7 +707,6 @@
   <project path="external/rust/crates/prettyplease" name="platform/external/rust/crates/prettyplease" groups="pdk" />
   <project path="external/rust/crates/proc-macro-error" name="platform/external/rust/crates/proc-macro-error" groups="pdk" />
   <project path="external/rust/crates/proc-macro-error-attr" name="platform/external/rust/crates/proc-macro-error-attr" groups="pdk" />
-  <project path="external/rust/crates/proc-macro-nested" name="platform/external/rust/crates/proc-macro-nested" groups="pdk" />
   <project path="external/rust/crates/proc-macro2" name="platform/external/rust/crates/proc-macro2" groups="pdk" />
   <project path="external/rust/crates/protobuf" name="platform/external/rust/crates/protobuf" groups="pdk" />
   <project path="external/rust/crates/protobuf-codegen" name="platform/external/rust/crates/protobuf-codegen" groups="pdk" />