ARM: dts: msm: Drop useless includes

Do not include skeleton.dtsi into feature-specific DTSI
files, since this will already be included by an
SoC-specific DTSI file.

Change-Id: I9565f0dada7b45a046888dfd1e569010d69d0693
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>