Drop non-prototype C function header variants: 'list' test case

Drop non-prototype C function header variants: 'list' test case

Remove old-style function header variants from list0.h and list1.c.
Fill the removed lines with comments or empty lines, such that the
line numbering is undisturbed.  Changes to the line numbering would
require heavy adjustments to list.exp, where many line numbers are
hard-coded, as well as a fair amount of knowledge about the source
code in and around certain lines.  Thus the dependency on the line
numbering can not be eliminated so easily, and it may not even be a
useful goal for a "list" test case.  Another option might be to adjust
the literal line numbers in list.exp, but even that is not as
straightforward as it may seem, since the test case expects certain
source lines to be exactly n lines apart.

gdb/testsuite/ChangeLog:

	* gdb.base/list0.h: Remove #ifdef PROTOTYPES, keep prototyped
	variant.  Preserve original line numbering.
	* gdb.base/list1.c: Likewise.