Cleanup TimeUtil.roundToSecond method

Timestamp is implied by the argument type, and the fact this is
in a TimeUtil class as a static method.

The entire method can be one line, the local variable provided no
value to any reader.

Style rules require spaces around operators such as '/'.

Change-Id: Ie312889502b86a82b2326d0f3f3fe1b0d43f4f55