clk: qcom: dispcc-qcm2290: get rid of test clock

The test clock apparently it's not used by anyone upstream. Remove it.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221228185237.3111988-9-dmitry.baryshkov@linaro.org