clk: qcom: Get rid of the test clock for dispcc-sc7180

The test clock isn't in the bindings and apparently it's not used by
anyone upstream.  Remove it.

Suggested-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lkml.kernel.org/r/20200203103049.v4.5.I28ac8f801456f1b950f7da10ed0f74a1344d4a35@changeid


Signed-off-by: Stephen Boyd <sboyd@kernel.org>