Fix schematic append clear annotation bug.

Clear the annotation of only the appended schematic and any sheets in it's
hierarchy.  Do not clear the annotation of the symbols in the target sheet.

Fixes lp:1805695

https://bugs.launchpad.net/kicad/+bug/1805695

eeschema/files-io.cpp

@@ -576,6 +576,8 @@ bool SCH_EDIT_FRAME::AppendSchematic()
         }
     }
 
+    newScreens.ClearAnnotation();
+
     // Check for duplicate sheet names in the current page.
     wxArrayString duplicateSheetNames;
     SCH_TYPE_COLLECTOR sheets;
@@ -622,7 +624,7 @@ bool SCH_EDIT_FRAME::AppendSchematic()
 
     // Clear all annotation in the imported schematic to prevent clashes with existing annotation.
     // Must be done after updating the symbol links as we need to know about multi-unit parts.
-    screens.ClearAnnotation();
+    // screens.ClearAnnotation();
 
     screens.TestDanglingEnds();