Removing SIconUpdateThreadTerminationError obsoleted by 1c687456 + Other long unused strings

(cherry picked from commit e89eb28b111fd8d4c0c3bd5ca7ce1af640afe8e7)

Source commit: 76a20d2abe088ebaa93d5ff7f7e698c0690ceda9

source/packages/filemng/CustomDirView.pas

@@ -490,7 +490,6 @@ type
   end;
 
 resourcestring
-  SErrorOpenFile = 'Can''t open file: ';
   SErrorRenameFile = 'Can''t rename file or directory: ';
   SErrorRenameFileExists = 'File already exists: ';
   SErrorInvalidName= 'Filename contains invalid characters:';
@@ -498,7 +497,6 @@ resourcestring
   STextFiles = '%u Files';
   STextDirectories = '%u Directories';
   SParentDir = 'Parent directory';
-  SIconUpdateThreadTerminationError = 'Can''t terminate icon update thread.';
   SDragDropError = 'DragDrop Error: %d';
   SDriveNotReady = 'Drive ''%s:'' is not ready.';
   SDirNotExists = 'Directory ''%s'' doesn''t exist.';

source/packages/filemng/CustomDriveView.pas

@@ -226,9 +226,6 @@ type
     property LastDDResult: TDragResult read FLastDDResult;
   end;
 
-resourcestring
-  SDragDropError = 'Drag&drop error: %d';
-
 implementation
 
 uses