Hide search from Compose on mobile devices (#7077)

* Hide search from Compose on mobile devices

We're presently seeing large numbers of users accidentally tooting what they're trying to search for. This PR hides the search form from the Compose view, now that we have a dedicated "search" tab on mobile.

* Don't "showSearch" on mobile if we're not currently searching (isSearchPage)

app/javascript/mastodon/features/compose/index.js

@@ -24,9 +24,9 @@ const messages = defineMessages({
   logout: { id: 'navigation_bar.logout', defaultMessage: 'Logout' },
 });
 
-const mapStateToProps = state => ({
+const mapStateToProps = (state, ownProps) => ({
   columns: state.getIn(['settings', 'columns']),
-  showSearch: state.getIn(['search', 'submitted']) && !state.getIn(['search', 'hidden']),
+  showSearch: ownProps.multiColumn ? state.getIn(['search', 'submitted']) && !state.getIn(['search', 'hidden']) : ownProps.isSearchPage,
 });
 
 @connect(mapStateToProps)
@@ -90,7 +90,7 @@ export default class Compose extends React.PureComponent {
       <div className='drawer'>
         {header}
 
-        <SearchContainer />
+        {(multiColumn || isSearchPage) && <SearchContainer /> }
 
         <div className='drawer__pager'>
           <div className='drawer__inner' onFocus={this.onFocus}>