Remove trailing newlines from help text

I noticed recently that some command had a trailing newline in its
"help" output.  So, I temporarily hacked cli-decode.c to print
something when a new command was installed that had a trailing newline
in its help message, and wrote this patch, which removes all the ones
I could find this way.  (There could still be a few more in *-nat
files.)

Tested on x86-64 Fedora 29.

gdb/ChangeLog
2019-06-11  Tom Tromey  <tromey@adacore.com>

	* infcall.c (_initialize_infcall): Remove trailing newline from
	help.
	* user-regs.c (_initialize_user_regs): Remove trailing newline
	from help.
	* typeprint.c (_initialize_typeprint): Remove trailing newline
	from help.
	* reverse.c (_initialize_reverse): Remove trailing newlines from
	help.
	* tracepoint.c (_initialize_tracepoint): Remove trailing newlines
	from help.
	* language.c (add_set_language_command): Remove trailing newline
	from help.
	* infcmd.c (_initialize_infcmd): Remove trailing newlines from
	help.
	* disasm.c (_initialize_disasm): Remove trailing newline from
	help.
	* top.c (init_main): Remove trailing newline from help.
	* interps.c (_initialize_interpreter): Remove trailing newline
	from help.
	* btrace.c (_initialize_btrace): Remove trailing newlines from
	help.
	* breakpoint.c (_initialize_breakpoint): Remove trailing newline
	from help.
	* python/python.c (_initialize_python): Remove trailing newline
	from help.
	* spu-tdep.c (_initialize_spu_tdep): Remove trailing newlines from
	help.
	* tui/tui-win.c (_initialize_tui_win): Remove trailing newlines
	from help.  Reformat some text.
	* tui/tui-stack.c (_initialize_tui_stack): Remove trailing newline
	from help.
	* tui/tui-layout.c (_initialize_tui_layout): Remove trailing
	newline from help.