Do not destroy GLSharedContextEflPrivate instance on exit.

Do not destroy GLSharedContextEflPrivate instance on exit.

Destructor of GLSharedContextEflPrivate instance is firing on content_shell_efl exit time.
This destructor is calling evas_gl_surface_destroy, but EFL at this time is deinitialized already
and calling this function causes segfault.

The solution is simply to not destory GLSharedContextEflPrivate instance (it's static global
object, and we are exiting anyway).
Reviewed by: Daniel Waślicki, Min-Soo Koo, Viatcheslav Ostapenko

Change-Id: I43f9608eafea1c7502ce1219e6c8a8576aa1face
Signed-off-by: Wojciech Wiśniewski <w.wisniewski@samsung.com>