Remove a comment in compile/compile-cplus-types.c

Remove a comment in compile/compile-cplus-types.c

The include sorter can't handle multi-line comments on the same line
as a #include.  This patch removes the only such comment.

In general I think these sorts of comments do not provide much value:
more often than not, I find that the comment is obsolete in one way or
another, and so the include sorter removes them in most cases.

gdb/ChangeLog
2019-01-22  Tom Tromey  <tom@tromey.com>

	* compile/compile-cplus-types.c: Remove a comment by #include.