compopt, disown, help, unset: move to common (#14029)

pages/common/unset.md

@@ -0,0 +1,16 @@
+# unset
+
+> Remove shell variables or functions.
+> More information: <https://manned.org/unset>.
+
+- Remove the variable `foo`, or if the variable doesn't exist, remove the function `foo`:
+
+`unset {{foo}}`
+
+- Remove the variables foo and bar:
+
+`unset -v {{foo}} {{bar}}`
+
+- Remove the function my_func:
+
+`unset -f {{my_func}}`