Fix localtime path and drop unneeded code

:Release Notes:
Fixed issue with using wrong path for updating time-zone and removed
code which tried to update /etc/localtime.

:Detailed Notes:
Since some devices may have read-only /etc folder we should move some
configuration files (that needs to be changed in run-time) to
/volatile place. Particularly /var/luna/preferences is more appropriate
place for localtime symlink.
/etc/localtime - is one of those configs that may need to be changed
after shipping device. Usually it is updated as a link to required
time-zone file. So we make it symlink to
/var/luna/preferences/localtime which in turn is symlink to actual
time-zone file.

Note that package that provides symlink in /etc/localtime should be
updated to get this thing working correctly.

:Testing Performed:
Verified with https://g2g.palm.com/3769 when time-zone changed:
- /etc/localtime points to /var/luna/preferences/localtime
- /var/luna/preferences/localtime points to selected time-zone rules file

:QA Notes:

:Issues Addressed:
[GF-44351] luna-sysservice can't change time-zone on squashfs image (read-only root)

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Change-Id: Icef246af5d825c7073177d686682ab121b704442
Reviewed-on: https://g2g.palm.com/3768
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Build Verification
Reviewed-by: Keith Derrick <keith.derrick@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>