Revert "all: rename module to pwdb"

This reverts commit 2d9ec0bf59.

The name `pwd` is still better, since it matches the name of the corresponding C header file.

pwd_test.v

@@ -0,0 +1,17 @@
+// vtest build: !windows
+import pwd
+
+fn test_get_by_uid() {
+	pw := pwd.get_by_uid(0)!
+	assert pw.name == 'root'
+}
+
+fn test_get_by_name() {
+	pw := pwd.get_by_name('root')!
+	assert pw.uid == 0
+}
+
+fn test_get_all() {
+	pws := pwd.get_all()
+	assert pws.len > 0
+}