[binutils-gdb] Remove unnecessary include from linespec.h

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT 8a76bd3ba43205b76226f41fe73e2840c2444742 ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: 8a76bd3ba43205b76226f41fe73e2840c2444742

Remove unnecessary include from linespec.h

linespec.h was inculding vec.h, but doesn't expose any VECs.
So, this include can be removed.

ChangeLog
2018-04-05  Tom Tromey  <tom@tromey.com>

	* linespec.h: Remove include of "vec.h".