Remove dated and misleading paragraph on headers

We no longer have any of the "Ports collection Makefile for...." lines,
so they do not need to be explained.

Differential:	https://reviews.freebsd.org/D23589
Submitted by:	salvadore (based on)
Reviewed by:	mat

documentation/content/en/books/porters-handbook/porting-samplem/chapter.adoc

@@ -35,7 +35,6 @@ The format shown is the recommended one for ordering variables, empty lines betw
 
 [.programlisting]
 ....
-[the header...just to make it easier for us to identify the ports.]
 # $FreeBSD$
 [ ^^^^^^^^^ This will be automatically replaced with RCS ID string by SVN
 when it is committed to our repository.  If upgrading a port, do not alter

documentation/content/en/books/porters-handbook/quick-porting/chapter.adoc

@@ -70,11 +70,6 @@ COMMENT=	Cat chasing a mouse all over the screen
 .include <bsd.port.mk>
 ....
 
-[NOTE]
-====
-In some cases, the [.filename]#Makefile# of an existing port may contain additional lines in the header, such as the name of the port and the date it was created. This additional information has been declared obsolete, and is being phased out.
-====
-
 Try to figure it out. Do not worry about the contents of the `$FreeBSD$` line, it will be filled in automatically by Subversion when the port is imported to our main ports tree. A more detailed example is shown in the <<porting-samplem,sample Makefile>> section.
 
 [[porting-desc]]