Remove unused introspection comment on the variable

[victoryforce]

This PR removes the unused introspection comment on the variable, because it is used as a regular variable, and not in functions that work with the introspection system (*_from_params). Functionally, it will not bring noticeable benefit (at most, throwing out an unnecessary string from the POT file). It is more about improving the quality, correctness and readability of the source code.

[jenshannoschwalm]

Hmm, i wouldn't say this is good. We certainly would want correct introspection information possibly for every parameter that gets committed - sure we are missing many still.

This would allow testing for buggy parameters inserted 'somehow' for example by incorrect presets. We had such problems.

[TurboGit]

I agree with @jenshannoschwalm !

[dterrahe]

functions that work with the introspection system (*_from_params).

Introspection is also used to initialise default_params (in dt_iop_default_init) and to show the tooltip with changes in the history module (_lib_history_change_text). This PR removes the default/changes it to zero. This would impact new images/module instances and when pressing module reset. Which would not be visible to the user, except in the history module. $DESCRIPTION is a user visible translatable string and should ideally not contain shortened words or underscores.