cmake: move deprecation definition to src/

There's no need to add the deprecation at the top-level.  Our tests add
deprecation explicitly.

CMakeLists.txt

@@ -103,10 +103,6 @@ include(DefaultCFlags)
 # Compiler / linker flags
 #
 
-if(DEPRECATE_HARD)
-	add_definitions(-DGIT_DEPRECATE_HARD)
-endif()
-
 if(NOT CMAKE_CONFIGURATION_TYPES)
 	# Build Debug by default
 	if(NOT CMAKE_BUILD_TYPE)

src/CMakeLists.txt

@@ -2,6 +2,10 @@ add_library(git2internal OBJECT)
 set_target_properties(git2internal PROPERTIES C_STANDARD 90)
 
 
+if(DEPRECATE_HARD)
+        add_definitions(-DGIT_DEPRECATE_HARD)
+endif()
+
 if(DEBUG_POOL)
 	set(GIT_DEBUG_POOL 1)
 endif()