test_dlopen: Remove extra -lpthread from LD_FLAGS for dltest{2}
test_dlopen: Remove extra -lpthread from LD_FLAGS for dltest{2}

dltest and dltest2 do not refer any symbols implemented
in pthread library, so do not explicitly link them with pthread.
It is required only for the shared objects that are loaded
via dlopen by those tests.

Signed-off-by: Filippo Arcidiacono <26825f07340f791bc0d38da89fcffcd93550a83c@st.com>
Signed-off-by: Carmelo Amoroso <532378793705a04edd56deb76ad8c0442834d55d@st.com>

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