thermal/drivers/tsens: Drop single-cell code for mdm9607

There is no dtsi file for mdm9607 in the kernel sources. Drop the
compatibility with unofficial dtsi and remove support for handling the
single-cell calibration data on mdm9607.

Cc: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>