thermal: ti-soc-thermal: remove dead code

Majority of this code (i.e. functions from ti-bandgap.c) has been
introduced in May 2013 by commit eb982001 ("thermal: introduce TI
SoC thermal driver"). Just remove it altogether (in case it is needed
it can be easily resurrected from git repo).

While at it fix incorrect "not used" comments.

Tested-by: Keerthy <j-keerthy@ti.com>
Acked-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>