Remove libcompos_client

CompOS APEX no longer needs to provide libcompos_client API (added
recently during T development).

Some of the code is still reusable, so the remaining code is moved to
composd/src/fd_server_helper.rs.

Bug: 205750213
Test: m
Test: atest ComposHostTestCases

Change-Id: I584b700c41ffc0e08c6ac6c171cb17ab21c7d8ff
diff --git a/compos/composd/src/composd_main.rs b/compos/composd/src/composd_main.rs
index f9751c3..57f64a5 100644
--- a/compos/composd/src/composd_main.rs
+++ b/compos/composd/src/composd_main.rs
@@ -19,6 +19,7 @@
 //! them, and orchestrating trusted compilation.
 
 mod compilation_task;
+mod fd_server_helper;
 mod instance_manager;
 mod instance_starter;
 mod internal_service;