Readd backspace char event for UI VM text fields

UI VMs expect a backspace char event, but sdl2 branch only was only sending a key event.
Revert cl_keys.c to master branch (it would cause backspace to happen twice in console).

code/client/cl_keys.c

@@ -441,19 +441,11 @@ void Field_KeyDownEvent( field_t *edit, int key ) {
 	switch ( key ) {
 		case K_DEL:
 			if ( edit->cursor < len ) {
-				memmove( edit->buffer + edit->cursor,
+				memmove( edit->buffer + edit->cursor, 
 					edit->buffer + edit->cursor + 1, len - edit->cursor );
 			}
 			break;
 
-		case K_BACKSPACE:
-			if ( edit->cursor > 0 ) {
-				memmove( edit->buffer + edit->cursor - 1,
-						edit->buffer + edit->cursor, len + 1 - edit->cursor );
-				edit->cursor--;
-			}
-			break;
-
 		case K_RIGHTARROW:
 			if ( edit->cursor < len ) {
 				edit->cursor++;

code/sdl/sdl_input.c

@@ -729,6 +729,9 @@ static void IN_ProcessEvents( void )
 				if( ( key = IN_TranslateSDLToQ3Key( &e.key.keysym, qtrue ) ) )
 					Com_QueueEvent( 0, SE_KEY, key, qtrue, 0, NULL );
 
+				if( key == K_BACKSPACE )
+					Com_QueueEvent( 0, SE_CHAR, CTRL('h'), 0, 0, NULL );
+
 				lastKeyDown = key;
 				break;