chore: enable client-side statement cache (#1496)

Author: olavloite

src/main/java/com/google/cloud/spanner/jdbc/JdbcDriver.java

@@ -191,8 +191,6 @@ public Connection connect(String url, Properties info) throws SQLException {
         if (matcher.matches()) {
           // strip 'jdbc:' from the URL, add any extra properties and pass on to the generic
           // Connection API
-          // TODO: Remove when statement cache should be enabled by default.
-          System.setProperty("spanner.statement_cache_size_mb", "0");
           String connectionUri = appendPropertiesToUrl(url.substring(5), info);
           ConnectionOptions options = ConnectionOptions.newBuilder().setUri(connectionUri).build();
           JdbcConnection connection = new JdbcConnection(url, options);