Fix vertical spacing in compact <ContextMenu> (#7684)

Fix https://github.com/vector-im/element-web/issues/20801

Regressed in https://github.com/matrix-org/matrix-react-sdk/pull/7339

Relevant styles were first added in https://github.com/matrix-org/matrix-react-sdk/pull/4858
(context behind why the original styles were added)

---

## Cause

Battling CSS specificity between the default and compact styles, https://specificity.keegan.st/

Known good (On `app.element.io` (expected)):
```css
// 0 3 0
.mx_IconizedContextMenu .mx_IconizedContextMenu_optionList .mx_AccessibleButton {
    padding-top: 12px;
    padding-bottom: 12px;
}

// Compact styles override our default rules because they come
// after the other styles (source order) and have the same specificity
// 0 3 0
.mx_IconizedContextMenu.mx_IconizedContextMenu_compact .mx_IconizedContextMenu_optionList > * {
    padding: 8px 16px 8px 11px;
}
```

Bad (On `develop` (broken)):
```css
// Default rules always override because they have higher specificity.
// The `:not()` selector doesn't add any extra specificity but the selectors inside the `:not(...)` do.
// 0 4 0
.mx_IconizedContextMenu .mx_IconizedContextMenu_optionList .mx_AccessibleButton:not(.mx_AccessibleButton_hasKind) {
    padding-top: 12px;
    padding-bottom: 12px;
}

// 0 3 0
.mx_IconizedContextMenu.mx_IconizedContextMenu_compact .mx_IconizedContextMenu_optionList > * {
    padding: 8px 16px 8px 11px;
}
```

src/components/views/messages/DateSeparator.tsx

@@ -193,7 +193,6 @@ export default class DateSeparator extends React.Component<IProps, IState> {
         if (this.state.contextMenuPosition) {
             contextMenu = <IconizedContextMenu
                 {...contextMenuBelow(this.state.contextMenuPosition)}
-                compact
                 onFinished={this.onContextMenuCloseClick}
             >
                 <IconizedContextMenuOptionList first>