rename eden_gc to eden_store_util

Summary:
Move this utility from eden/fs/service to eden/fs/store, and rename it to
`eden_store_util`.

I originally put it in the `service` subdirectory since it depends on library
code from `service/`, and most of the other code in `store/` shouldn't depend
on code in `service/`.  However logically it makes sense to be in the `store/`
directory.

I plan to update in the future to be able to perform some additionally utility
operations besides just garbage collection, so rename it to the more generic
`eden_store_util` name.

Reviewed By: chadaustin

Differential Revision: D15043209

fbshipit-source-id: e6c4a874ddd05bd1576ea2e8a6c6156ccdf4628f

eden/fs/service/CMakeLists.txt

@@ -16,7 +16,6 @@ add_thrift_cpp2_library(
 )
 
 file(GLOB SERVICE_SRCS "*.cpp")
-list(REMOVE_ITEM SERVICE_SRCS "${CMAKE_CURRENT_SOURCE_DIR}/eden_gc.cpp")
 add_library(
   eden_service STATIC
     ${SERVICE_SRCS}

eden/fs/store/CMakeLists.txt

@@ -1,4 +1,8 @@
 file(GLOB STORE_SRCS "*.cpp")
+list(
+  REMOVE_ITEM SERVICE_SRCS
+  "${CMAKE_CURRENT_SOURCE_DIR}/eden_store_util.cpp"
+)
 add_library(
   eden_store STATIC
     ${STORE_SRCS}