I noticed that cli_style_option declares a constructor that is never
defined. This removes it.
gdb/ChangeLog
2019-11-10 Tom Tromey <tom@tromey.com>
* cli/cli-style.h (class cli_style_option) <cli_style_option>:
Remove unused declaration.
Change-Id: Ic59ec7eab4d7183d9392b58709354b2d4449b7be