Remove the hack for dynamically linking the runtime for FFmpeg as it's been fixed upstream

aegisub/build/ffmpeg/dynamic_msvcrt.h

@@ -1,34 +0,0 @@
-// Copyright (c) 2012, Thomas Goyne <plorkyeran@aegisub.org>
-//
-// Permission to use, copy, modify, and distribute this software for any
-// purpose with or without fee is hereby granted, provided that the above
-// copyright notice and this permission notice appear in all copies.
-//
-// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
-// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
-// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
-// ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
-// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
-// ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
-// OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
-//
-// Aegisub Project http://www.aegisub.org/
-
-// FFmpeg/libav replace these standard library functions with their own
-// implementations by #defining them to avpriv_fn, which results in them
-// being declared as __declspec(dllimport) when dynamically linking the
-// runtime. To fix this, redeclare them correctly.
-
-#include <stdarg.h>
-#include <stdio.h>
-#include <string.h>
-
-// Disable the inconsistent dll linkage warning since that's the entire
-// point of this
-#pragma warning( push )
-#pragma warning( disable: 4273 )
-int avpriv_snprintf(char *s, size_t n, const char *fmt, ...);
-int avpriv_vsnprintf(char *s, size_t n, const char *fmt, va_list ap);
-double avpriv_strtod(const char *nptr, char **endptr);
-#pragma warning( pop )
-

aegisub/build/ffmpeg/ffmpeg.vcxproj

@@ -40,7 +40,6 @@
       --extra-cflags=-D_SYSCRT
       --extra-cflags=-wd4005
       --extra-cflags=-wd4189
-      --extra-cflags=-FIdynamic_msvcrt.h
       --toolchain=msvc
       $(CfgDebug)
     </CfgArgs>