Remove all blank "Modified by:" lines from top comment blocks

Having this line is not useful at all as it doesn't contain any
information and shouldn't be filled in the future as git-shortlog can
provide the information about people who changed the given file more
more reliably than consulting the comments in any case.

Keep the non-blank lines for historical purposes.

utils/helpview/src/helpview.cpp

@@ -3,7 +3,6 @@
 // Purpose:     HelpView application
 //              A standalone viewer for wxHTML Help (.htb) files
 // Author:      Vaclav Slavik, Julian Smart
-// Modified by:
 // Created:     2002-07-09
 // Copyright:   (c) 2002 Vaclav Slavik, Julian Smart and others
 // Licence:     wxWindows licence

utils/helpview/src/helpview.h

@@ -2,7 +2,6 @@
 // Name:        helpview.h
 // Purpose:     HelpView application class
 // Author:      Vaclav Slavik, Julian Smart
-// Modified by:
 // Created:     2002-07-09
 // Copyright:   (c) 2002 Vaclav Slavik, Julian Smart and others
 // Licence:     wxWindows licence

utils/helpview/src/remhelp.cpp

@@ -2,7 +2,6 @@
 // Name:        remhelp.cpp
 // Purpose:     Remote help controller class
 // Author:      Eric Dowty
-// Modified by:
 // Created:     2002-11-18
 // Copyright:   (c) Julian Smart
 // Licence:     wxWindows licence

utils/helpview/src/remhelp.h

@@ -2,7 +2,6 @@
 // Name:        remhelp.h
 // Purpose:     Remote help controller class
 // Author:      Eric Dowty
-// Modified by:
 // Created:     2002-11-18
 // Copyright:   (c) Julian Smart
 // Licence:     wxWindows licence