ffmpeg: Monster cleanup, move prefix to "legacy".

This breaks the build of Haiku (if you were to try to compile it with
these packages). I'm going to clean that up next.

media-video/ffmpeg/patches/ffmpeg-2.3.patch

@@ -1,25 +0,0 @@
-From b44fcd01d625972a8a4ee18cb72be1d0bd4cde38 Mon Sep 17 00:00:00 2001
-From: Augustin Cavalier <waddlesplash@gmail.com>
-Date: Mon, 28 Jul 2014 15:54:14 -0400
-Subject: [PATCH] configure: remove invalid option. From a StackOverflow post.
-
----
- configure | 2 +-
- 1 file changed, 1 insertion(+), 1 deletion(-)
-
-diff --git a/configure b/configure
-index 4ed43a0..6a81e3b 100755
---- a/configure
-+++ b/configure
-@@ -4297,7 +4297,7 @@ void foo(void) { __asm__ volatile ("" ::); }
- EOF
- 
- _restrict=
--for restrict_keyword in restrict __restrict__ __restrict; do
-+for restrict_keyword in __restrict__ __restrict; do
-     check_cc <<EOF && _restrict=$restrict_keyword && break
- void foo(char * $restrict_keyword p);
- EOF
--- 
-1.8.3.4
-