Using toolbarLayout property of pe:pageCustomizable you can choose which parts of composer you want to show.
Removing "button" property from the list will remove Save button (in case of Sandbox enabled) and Close button.
I don't know if it's help you, but you can add Save Sandbox button by yourself if it's necessary.
That was the exact thing i was looking for thank you ! For folks who come across similar customization use case , here is what i did,
For pe:pageCustomizable component in your page, goto property inspector --> Appearance tab --> toolbarLayout --> message stretch statusindicator newline menu addonpanels stretch help newline concurrencymessage
Here is the complete list for toolbarLayout - message stretch statusindicator newline menu addonpanels button stretch help newline concurrencymessage