build: Make bitcoin_ipc_test depend on bitcoin_ipc

This change is needed to allow generated capnp code in src/ipc/capnp/ to be
used in unit tests for better test coverage in upcoming commits.

src/test/CMakeLists.txt

@@ -160,14 +160,6 @@ if(ENABLE_WALLET)
 endif()
 
 if(WITH_MULTIPROCESS)
-  add_library(bitcoin_ipc_test STATIC EXCLUDE_FROM_ALL
-    ipc_test.cpp
-  )
-
-  target_capnp_sources(bitcoin_ipc_test ${PROJECT_SOURCE_DIR}
-    ipc_test.capnp
-  )
-
   target_link_libraries(bitcoin_ipc_test
     PRIVATE
       core_interface