Remove explicit width for search field input

Alabaster does not need to adapt the width. Geometry is handled by the basic theme.  In fact, this could cause wrapping of the search button for some magnifications.

alabaster/static/alabaster.css_t

@@ -215,10 +215,6 @@ div.sphinxsidebar input {
     font-size: 1em;
 }
 
-div.sphinxsidebar #searchbox input[type="text"] {
-    width: 160px;
-}
-
 div.sphinxsidebar .search > div {
     display: table-cell;
 }