scripts/kernel-doc: Remove duplicated DOC: start handling

Further up in the state machinery we switch from STATE_NAME to
STATE_DOCBLOCK when we match /$doc_block/. Which means this block of
code here is entirely unreachable, unless there are multiple DOC:
sections within a single kernel-doc comment.

Getting a list of all the files with more than one DOC: section using

$ git grep -c " * DOC:" | grep -v ":1$"

and then doing a full audit of them reveals there are no such comment
blocks in the kernel.

Supporting multiple DOC: sections in a single kernel-doc comment does
not seem like a recommended way of doing things anyway, so nuke the code
for simplicity.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: linux-doc@vger.kernel.org
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
[Jani: amended the commit message]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

scripts/kernel-doc

@@ -2942,24 +2942,7 @@ sub process_file($) {
 		process_state3_type($_, $file);
 	    }
 	} elsif ($state == STATE_DOCBLOCK) {
-		# Documentation block
-		if (/$doc_block/) {
-			dump_doc_section($file, $section, xml_escape($contents));
-			$contents = "";
-			$function = "";
-			%parameterdescs = ();
-			%parametertypes = ();
-			@parameterlist = ();
-			%sections = ();
-			@sectionlist = ();
-			$prototype = "";
-			if ( $1 eq "" ) {
-				$section = $section_intro;
-			} else {
-				$section = $1;
-			}
-		}
-		elsif (/$doc_end/)
+		if (/$doc_end/)
 		{
 			dump_doc_section($file, $section, xml_escape($contents));
 			$section = $section_default;