improve copy_bytes() maintenance

Remove the copy_bytes() function from files.c and util/recover.c
and place a single copy into hacklib.

sys/unix/NetHack.xcodeproj/project.pbxproj

@@ -1872,6 +1872,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				059660BE2C80B00400398EDE /* hacklib.c in Sources */,
 				31B8A45221A26A750055BD01 /* recover.c in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;