Cocoa: Fix install name for installed dylib

The install name was incorrectly set to a relative path.

This change leaves the install name of the installed dylib as
@rpath/soname.  Those who wish to override this can set the
CMAKE_INSTALL_NAME_DIR variable.

Closes #1504.

(cherry picked from commit 384ff74a4645347bbc5726fc572138b38f87ae8b)

src/CMakeLists.txt

@@ -168,9 +168,6 @@ if (BUILD_SHARED_LIBS)
     elseif (APPLE)
         # Add -fno-common to work around a bug in Apple's GCC
         target_compile_options(glfw PRIVATE "-fno-common")
-
-        set_target_properties(glfw PROPERTIES
-                              INSTALL_NAME_DIR "${CMAKE_INSTALL_LIBDIR}")
     endif()
 
     if (UNIX)