Remove `-c` class name filter

[paul-bennett]

Since Juggle now supports searching for classes directly ($ juggle class /foo/i), this option is no longer relevant. Besides, it has never applied to declaration-style member searches.

Remove -c/--class-name.

Related issues:

• -c will be reused as a shorthand for the --conversions option (#58)
• This feature may be reintroduced with a long name (--class-filter), and in a more comprehensive/structured way if --package-filter is implemented (#77)

[paul-bennett]

Original --class-name filter will be removed by paul-bennett/juggle-2#92.