Revert "Fix deprecated readDataToEndOfFile API"

This reverts commit dc280a1.

Author: franklinsch

Sources/markdown-tool/main.swift

@@ -30,20 +30,15 @@ struct MarkdownCommand: ParsableCommand {
     ])
 
     static func parseFile(at path: String, options: ParseOptions) throws -> (source: String, parsed: Document) {
-        let data = try Data(contentsOf: URL(fileURLWithPath: path))
+        let data = try Data(contentsOf: URL( fileURLWithPath: path))
         guard let inputString = String(data: data, encoding: .utf8) else {
             throw Error.couldntDecodeInputAsUTF8
         }
         return (inputString, Document(parsing: inputString, options: options))
     }
 
     static func parseStandardInput(options: ParseOptions) throws -> (source: String, parsed: Document) {
-        let stdinData: Data
-        if #available(macOS 10.15.4, *) {
-            stdinData = try FileHandle.standardInput.readToEnd() ?? Data()
-        } else {
-            stdinData = FileHandle.standardInput.readDataToEndOfFile()
-        }
+        let stdinData = FileHandle.standardInput.readDataToEndOfFile()
         guard let stdinString = String(data: stdinData, encoding: .utf8) else {
             throw Error.couldntDecodeInputAsUTF8
         }