Remove GMT time zones - they are the same as UTC

As stated in the original discussion [1], "GMT tracks UTC and this is not
expected to change".

Originally fixed in Quozl's patch [1] in relation to issue #2195.

[1]: http://lists.sugarlabs.org/archive/sugar-devel/2011-March/030497.html
Include all UTC time zones

Fixes the issue where places like Tonga have their time zones excluded. They
need the UTC+13 and +14 instead of -11 and -10, as they are on the the other
side of the international date line to the -11 and -10 time zones.

This fix is related to bug #2195 and is based of Quozl's patch [1].
TL;DR: "increase UTC timezone coverage for Kiribati and Tonga." [1]

[1]: http://lists.sugarlabs.org/archive/sugar-devel/2011-March/030497.html
Fix UTC time handeling, fixes #2195

Using the solution suggested by Sascha Silbe [1].  TL;DR "All of the
UTC+X UTC-X timezones could be translated into entries in
/usr/share/zoneinfo/Etc. For example, "UTC-5" would be converted to
TZ=:Etc/GMT+5"

Simmilar to Quozl's patch [2].  Quozl explains his patch as "translating
from ISO 8601 to POSIX.1 format, by reversing the sign"

[1]: http://lists.sugarlabs.org/archive/sugar-devel/2011-March/030532.html
[2]: http://lists.sugarlabs.org/archive/sugar-devel/2011-March/030497.html