Remove "extern C" declaration when importing libgit2

libgit2 takes care of thiss now, so we don't have to.

PBGitGrapher.mm

@@ -6,15 +6,12 @@
 //  Copyright 2008 __MyCompanyName__. All rights reserved.
 //
 
-extern "C" {
-#import "git/oid.h"
-}
-
 #import "PBGitGrapher.h"
 #import "PBGitCommit.h"
 #import "PBGitLane.h"
 #import "PBGitGraphLine.h"
 #import <list>
+#import "git/oid.h"
 
 using namespace std;
 

PBGitLane.h

@@ -6,10 +6,7 @@
 //  Copyright 2008 __MyCompanyName__. All rights reserved.
 //
 #import <Cocoa/Cocoa.h>
-extern "C"
-{
 #include "git/oid.h"
-}
 
 class PBGitLane {
 	static int s_colorIndex;

PBGitRevList.mm

@@ -6,17 +6,13 @@
 //  Copyright 2008 __MyCompanyName__. All rights reserved.
 //
 
-extern "C"
-{
-#include "git/oid.h"
-}
-
 #import "PBGitRevList.h"
 #import "PBGitRepository.h"
 #import "PBGitCommit.h"
 #import "PBGitGrapher.h"
 #import "PBGitRevSpecifier.h"
 
+#include "git/oid.h"
 #include <ext/stdio_filebuf.h>
 #include <iostream>
 #include <string>