DevCachefiles: remove unused method IsInUse()

Since "cull" has the same checks, I don't think we'll ever need the
"inuse" command.

src/DevCachefiles.cxx

@@ -10,39 +10,6 @@
 
 #include <limits.h> // for NAME_MAX
 
-#if 0
-// TODO does this now work because of the cachefiles CWD problem
-[[gnu::pure]]
-static Co::Task<bool>
-IsInUse(Uring::Queue &uring, FileDescriptor dev_cachefiles, std::string_view filename)
-try {
-	if (filename.size() >= NAME_MAX)
-		co_return false;
-
-	// unfortunately, fscache is buggy with writev()
-	const auto buffer = FmtBuffer<NAME_MAX + 8>("inuse {}", filename);
-
-	co_await Uring::CoWrite(uring, dev_cachefiles,
-				AsBytes(std::string_view{buffer}), 0);
-	co_return false;
-} catch (const std::system_error &e) {
-	co_return IsErrno(e, EBUSY);
-}
-#endif
-
-bool
-DevCachefiles::IsInUse(std::string_view filename) noexcept
-{
-	if (filename.size() >= NAME_MAX)
-		return false;
-
-	// unfortunately, fscache is buggy with writev()
-	const auto buffer = FmtBuffer<NAME_MAX + 8>("inuse {}", filename);
-
-	return fd.Write(AsBytes(std::string_view{buffer})) < 0 &&
-		errno == EBUSY;
-}
-
 DevCachefiles::CullResult
 DevCachefiles::CullFile(std::string_view filename) noexcept
 {

src/DevCachefiles.hxx

@@ -22,9 +22,6 @@ public:
 	DevCachefiles(const DevCachefiles &) = delete;
 	DevCachefiles &operator=(const DevCachefiles &) = delete;
 
-	[[gnu::pure]]
-	bool IsInUse(std::string_view filename) noexcept;
-
 	enum class CullResult {
 		SUCCESS,
 		BUSY,