Remove some text from --version output

Remove some text from --version output

I happened to notice recently that "gdb --version" says:

    GNU gdb (GDB) 8.0.50.20170911-git
    Copyright (C) 2017 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
    and "show warranty" for details.
    This GDB was configured as "x86_64-pc-linux-gnu".
    Type "show configuration" for configuration details.
    For bug reporting instructions, please see:
    <http://www.gnu.org/software/gdb/bugs/>.
    Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.
    For help, type "help".
    Type "apropos word" to search for commands related to "word".

This is a bit on the wordy side, but also references interactive
commands, which I think doesn't really make sense for --version.

This patch removes some text from --version, while leaving it in the
"show version" output.  It also adds a newline between the URLs and
the "For help, ..." text, because I thought that was easier to read.
Finally, it indents one of the URLs, since that was simpler to read,
but not the other URL, because the current format is specified by the
GNU coding standards section on "--version".

Now the --version output looks like:

    GNU gdb (GDB) 8.1.50.20180511-git
    Copyright (C) 2018 Free Software Foundation, Inc.
    License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
    This is free software: you are free to change and redistribute it.
    There is NO WARRANTY, to the extent permitted by law.

Tested by the buildbot.

gdb/ChangeLog
2018-06-05  Tom Tromey  <tom@tromey.com>

	* cli/cli-cmds.c (show_version): Update.
	* top.c (print_gdb_version): Add "interactive" parameter.
	Update.
	* main.c (captured_main_1): Update.
	* top.h (print_gdb_version): Add "interactive" parameter and a
	comment.

gdb/testsuite/ChangeLog
2018-06-05  Tom Tromey  <tom@tromey.com>

	* gdb.base/default.exp: Update expected "show version" output.