indent(1): Remove dead code relating to unix-style comments.

The original indent(1) described unix-style comments as similar to box
comments, except the first non-blank character on each line is lined up
with the '*' of the "/*" which appears on a line by itself.

The code has been turned off for ages and -sc/-nsc make it even
less relevant.

Reference:
https://github.com/pstef/freebsd_indent/commit/89c5fe2c56742d96975bb3ea6b99f28baf9d82f6

Differential Revision: https://reviews.freebsd.org/D6966 (Partial)

Submitted by: Piotr Stefaniak