There is no dtsi file for msm8939 in the kernel sources. Drop the
compatibility with unofficial dtsi and remove support for handling the
single-cell calibration data on msm8939.

Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: NBryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: NKonrad Dybcio <konrad.dybcio@linaro.org>
Acked-by: NShawn Guo <shawn.guo@linaro.org>
Signed-off-by: NDmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230101194034.831222-14-dmitry.baryshkov@linaro.orgSigned-off-by: NDaniel Lezcano <daniel.lezcano@linaro.org>