Update #4455, Regenerate all commands' docs (#4557)

docs/commands/dfr_drop-duplicates.md

@@ -0,0 +1,24 @@
+---
+title: dfr drop-duplicates
+layout: command
+version: 0.59.0
+---
+
+Drops duplicate values in dataframe
+
+## Signature
+
+```> dfr drop-duplicates (subset) --maintain```
+
+## Parameters
+
+ -  `subset`: subset of columns to drop duplicates
+ -  `--maintain`: maintain order
+
+## Examples
+
+drop duplicates
+```shell
+> [[a b]; [1 2] [3 4] [1 2]] | dfr to-df | dfr drop-duplicates
+```
+