Gripper check now uses firmware build date.

Gripper version 1.1.242 is the legacy gripper version,
and other 1.x.x grippers are invalid firmware versions. To avoid the
clashing of Manufacturing 1.x.x grippers and RSDK 1.1.x gripper
versions, I switched the check use gripper firmware dates. That way, any
recently built manufacturing or RSDK gripper will pass without warning
or error. Older build versions will warn, and any date as far back as a
bad firmware version will fail.

Also, removed deprecated Gripper.hardware_version() function.
The original concept makes sense. Now, with SDK release being ~1 month after manufacturing, these date checks should allow for both coupled Manufacturing and SDK versions to pass without warning. That is because the "warn" date should be the previous SDK release date, and that is presumable before the most recent coupled manufacturing release. The "fail" date should be the SDK release date closest to the first know bad Gripper Firmware Version (here that's 0.6.2). It gets quite complex if we start saying that old versions of the Gripper Firmware are selectively OK, because their dates could be mixed right in with bad version dates. The safer approach would be to warn up until a bad firmware version and then error out any further back. Since bad firmware is something we are actively avoiding, this feature should be used infrequently. Also, I'm totally fine with patching "OK" dates back in later when/if they are needed.