lib/fmt: require libfmt 9

Version 9 added the "debug format" which I'd like to use.

src/client/Response.cxx

@@ -28,11 +28,7 @@ bool
 Response::VFmt(fmt::string_view format_str, fmt::format_args args) noexcept
 {
 	fmt::memory_buffer buffer;
-#if FMT_VERSION >= 80000
 	fmt::vformat_to(std::back_inserter(buffer), format_str, args);
-#else
-	fmt::vformat_to(buffer, format_str, args);
-#endif
 	return Write(buffer.data(), buffer.size());
 }
 

src/client/Response.hxx

@@ -1,15 +1,11 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 // Copyright The Music Player Daemon Project
 
-#ifndef MPD_RESPONSE_HXX
-#define MPD_RESPONSE_HXX
+#pragma once
 
 #include "protocol/Ack.hxx"
 
 #include <fmt/core.h>
-#if FMT_VERSION >= 80000 && FMT_VERSION < 90000
-#include <fmt/format.h>
-#endif
 
 #include <cstddef>
 #include <span>
@@ -66,14 +62,8 @@ public:
 
 	template<typename S, typename... Args>
 	bool Fmt(const S &format_str, Args&&... args) noexcept {
-#if FMT_VERSION >= 90000
 		return VFmt(format_str,
 			    fmt::make_format_args(args...));
-#else
-		return VFmt(fmt::to_string_view(format_str),
-			    fmt::make_args_checked<Args...>(format_str,
-							    args...));
-#endif
 	}
 
 	/**
@@ -92,15 +82,7 @@ public:
 	template<typename S, typename... Args>
 	void FmtError(enum ack code,
 		      const S &format_str, Args&&... args) noexcept {
-#if FMT_VERSION >= 90000
 		return VFmtError(code, format_str,
 				 fmt::make_format_args(args...));
-#else
-		return VFmtError(code, fmt::to_string_view(format_str),
-				 fmt::make_args_checked<Args...>(format_str,
-								 args...));
-#endif
 	}
 };
-
-#endif