ARM: dts: msm: Remove thermal node property from VADC nodes for SDM670

Remove the property "vadc-thermal-node" from VADC nodes as it leads
to failure of thermal registration for many ADC channels on SDM670.

Change-Id: I4d032c9c3a68ec067614d48a59850323d84b8f45
Signed-off-by: Jishnu Prakash <jprakash@codeaurora.org>