Fix memory leak in axTime3.cc

[taldcroft]

Implements fix suggested by @mbaski in #31 to fix a memory leak that has been there for at least 12 years (!).

Testing:

• Confirmed that this fixes the memory leak on Mac using the code snippet in Memory leak in C++ code #31 and watching memory with top. Also reproduced the leak without this fix.
• Passes unit tests on ska3-flight on Mac, HEAD CentOS-5 and HEAD CentOS-6.

FYI Chandra.Time is not building on CentOS-6. Not a problem since 5 is still the official build platform, but will need to fix eventually.

Fixes #31

[mbaski]

On Windows, the unit tests pass successfully, the thermal models work as expected in MCC, and the memory leak appears to be fixed.