lib: remove file timestamp rounding hack

Introduced in commit 9836cf5 ("lib: lazy instantiation of fs.Stats
dates") without providing any rationale - that wasn't added until later,
by someone else - and it doesn't look the least bit correct to me.

It certainly makes an upcoming regression test fail because a timestamp
in the deep past doesn't round-trip correctly, it's off by a fraction of
a second.

Refs: nodejs#32369

lib/internal/fs/utils.js

@@ -362,16 +362,6 @@ function nsFromTimeSpecBigInt(sec, nsec) {
   return sec * kNsPerSecBigInt + nsec;
 }
 
-// The Date constructor performs Math.floor() to the timestamp.
-// https://www.ecma-international.org/ecma-262/#sec-timeclip
-// Since there may be a precision loss when the timestamp is
-// converted to a floating point number, we manually round
-// the timestamp here before passing it to Date().
-// Refs: https://github.com/nodejs/node/pull/12607
-function dateFromMs(ms) {
-  return new Date(Number(ms) + 0.5);
-}
-
 function BigIntStats(dev, mode, nlink, uid, gid, rdev, blksize,
                      ino, size, blocks,
                      atimeNs, mtimeNs, ctimeNs, birthtimeNs) {
@@ -386,10 +376,10 @@ function BigIntStats(dev, mode, nlink, uid, gid, rdev, blksize,
   this.mtimeNs = mtimeNs;
   this.ctimeNs = ctimeNs;
   this.birthtimeNs = birthtimeNs;
-  this.atime = dateFromMs(this.atimeMs);
-  this.mtime = dateFromMs(this.mtimeMs);
-  this.ctime = dateFromMs(this.ctimeMs);
-  this.birthtime = dateFromMs(this.birthtimeMs);
+  this.atime = new Date(Number(this.atimeMs));
+  this.mtime = new Date(Number(this.mtimeMs));
+  this.ctime = new Date(Number(this.ctimeMs));
+  this.birthtime = new Date(Number(this.birthtimeMs));
 }
 
 ObjectSetPrototypeOf(BigIntStats.prototype, StatsBase.prototype);
@@ -412,10 +402,10 @@ function Stats(dev, mode, nlink, uid, gid, rdev, blksize,
   this.mtimeMs = mtimeMs;
   this.ctimeMs = ctimeMs;
   this.birthtimeMs = birthtimeMs;
-  this.atime = dateFromMs(atimeMs);
-  this.mtime = dateFromMs(mtimeMs);
-  this.ctime = dateFromMs(ctimeMs);
-  this.birthtime = dateFromMs(birthtimeMs);
+  this.atime = new Date(atimeMs);
+  this.mtime = new Date(mtimeMs);
+  this.ctime = new Date(ctimeMs);
+  this.birthtime = new Date(birthtimeMs);
 }
 
 ObjectSetPrototypeOf(Stats.prototype, StatsBase.prototype);