thermal: exynos: remove dead code for HW_MODE calibration

The commit 1928457e

 ("thermal: exynos: Add hardware mode thermal
calibration support") has added HW_MODE feature but it has never
been enabled.  As such it has been a dead code for over a year
now and should be removed from the kernel.

We don't keep the unused/untested features in the kernel just
in case that some future hardware might need it.  Such code has
a real maintainance cost (all other code changes have to take
the dead code into account) and usually makes future changes
more difficult, not easier (i.e. recent additions of Exynos5420
SoC and Exynos5260 SoC thermal support has not made use of any
of the driver's currently unused/untested features, moreover
the recently added code is more complex than needed because of
the existing dead code).  Also all removed dead code is still
accessible in the kernel git repository and can be easily
brought back if/when needed.

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Tested-by: Amit Daniel Kachhap <amit.daniel@samsung.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>