CMake: Don't try to set property on target before it is defined.

The exact same code this commit removes is repeated in line 748.
There, it actually works, since the "assimp" target is defined there.

code/CMakeLists.txt

@@ -656,11 +656,6 @@ if ( MSVC )
   ADD_DEFINITIONS( -D_CRT_SECURE_NO_WARNINGS )
 endif ( MSVC )
 
-if (APPLE)
-  SET_TARGET_PROPERTIES( assimp PROPERTIES
-    INSTALL_NAME_DIR "${CMAKE_INSTALL_PREFIX}/${LIB_INSTALL_DIR}"
-  )
-endif()
 if (UNZIP_FOUND)
   SET (unzip_compile_SRCS "")
 else (UNZIP_FOUND)