fixup! Enable content shell with aura for desktop

fixup! Enable content shell with aura for desktop

This patch reverts a change related to ThreadLocalStorage 'tls_model'
done in patch [1], as the change was causing error [2] when our
chromium-efl library is being loaded with dlopen from another library.

As per the comment description mentioned in file
third_party/blink/renderer/platform/heap/thread_local.h, it is suggested
to use "local-exec" type for Linux platform, hence reverting back to
original type, which avoids the error [2].

[1] https://review.tizen.org/gerrit/284216

[2] "cannot allocate memory in static tls block"

Change-Id: I683859fff133217eec91e285a09d9430e6c4d4e7
Signed-off-by: Gajendra N <gajendra.n@samsung.com>