weeding: remove another unnecessary setting of openfile->current_y

The setting of current_y in copy_from_filestruct() also appears to be
a holdover from the days of a more-common STATIONARY scrolling mode.

do_cut_text() uses the above function when copying text (uncutting
text again right after cutting it).  Since the text is effectively
the same afterward, current_y doesn't need to change.

do_uncut_text(), however, does need current_y up to date in one case:
when uncutting a full screen or less' worth of lines, focusing will be
FALSE, and it uses edit_refresh(), so it will use STATIONARY scrolling
mode then.  Take a cue from do_insertfile() and call reset_cursor() to
get an updated current_y.

(Note that the check for a full screen or less' worth of lines uses
incorrect values when in softwrap mode, but that's a separate problem.)

undo_cut(), do_redo(), and backup_lines() do not need set current_y
because they all result in edit_refresh() with focusing = TRUE, so
they do a CENTERING scroll which does ...

src/cut.c

@@ -284,6 +284,9 @@ void do_uncut_text(void)
     /* Mark the file as modified. */
     set_modified();
 
+    /* Update the cursor position to account for the inserted lines. */
+    reset_cursor();
+
     refresh_needed = TRUE;
 
 #ifndef DISABLE_COLOR

src/nano.c

@@ -469,11 +469,6 @@ void copy_from_filestruct(filestruct *somebuffer)
     /* Add the number of characters in the copied text to the file size. */
     openfile->totsize += get_totsize(openfile->fileage, openfile->filebot);
 
-    /* Update the current y-coordinate to account for the number of
-     * lines the copied text has, less one since the first line will be
-     * tacked onto the current line. */
-    openfile->current_y += openfile->filebot->lineno - 1;
-
     /* If we pasted onto the first line of the edit window, the corresponding
      * struct has been freed, so... point at the start of the copied text. */
     if (edittop_inside)