Remove extern declarations in .c files, .h files have them.

Remove extern declarations in .c files, .h files have them.
* src/data.c:
* src/dired.c:
* src/editfns.c:
* src/filelock.c:
* src/fns.c:
* src/font.c:
* src/fontset.c:
* src/frame.c:
* src/fringe.c:
* src/ftfont.c:
* src/gtkutil.c:
* src/indent.c:
* src/keyboard.c:
* src/keymap.c:
* src/lread.c:
* src/menu.c:
* src/print.c:
* src/search.c:
* src/sound.c:
* src/window.c:
* src/xdisp.c:
* src/xfaces.c:
* src/xfns.c:
* src/xfont.c:
* src/xftfont.c:
* src/xmenu.c:
* src/xterm.c: Remove declarations.