Revert "add share index"

This reverts commit e19b3a8794.

db_structure.xml

@@ -942,18 +942,6 @@
 					<sorting>ascending</sorting>
 				</field>
 			</index>
-			<index>
-				<name>file_target_index</name>
-				<field>
-					<name>file_target</name>
-				</field>
-				<field>
-					<name>uid_owner</name>
-				</field>
-				<field>
-					<name>share_type</name>
-				</field>
-			</index>
 		</declaration>
 
 	</table>