Remove duplicating declaration of git_email_create_from_diff()

Exactly the same function already declared in include/git2/email.h

include/git2/email.h

@@ -84,30 +84,6 @@ typedef struct {
 	GIT_DIFF_FIND_OPTIONS_INIT \
 }
 
-/**
- * Create a diff for a commit in mbox format for sending via email.
- *
- * @param out buffer to store the e-mail patch in
- * @param diff the changes to include in the email
- * @param patch_idx the patch index
- * @param patch_count the total number of patches that will be included
- * @param commit_id the commit id for this change
- * @param summary the commit message for this change
- * @param body optional text to include above the diffstat
- * @param author the person who authored this commit
- * @param opts email creation options
- */
-GIT_EXTERN(int) git_email_create_from_diff(
-	git_buf *out,
-	git_diff *diff,
-	size_t patch_idx,
-	size_t patch_count,
-	const git_oid *commit_id,
-	const char *summary,
-	const char *body,
-	const git_signature *author,
-	const git_email_create_options *opts);
-
 /**
  * Create a diff for a commit in mbox format for sending via email.
  * The commit must not be a merge commit.

src/libgit2/diff.c

@@ -16,7 +16,7 @@
 #include "diff_generate.h"
 
 #include "git2/version.h"
-#include "git2/email.h"
+#include "git2/sys/email.h"
 
 struct patch_id_args {
 	git_diff *diff;

src/libgit2/email.c

@@ -16,6 +16,7 @@
 
 #include "git2/email.h"
 #include "git2/patch.h"
+#include "git2/sys/email.h"
 #include "git2/version.h"
 
 /*

tests/libgit2/email/create.c

@@ -1,5 +1,6 @@
 #include "clar.h"
 #include "clar_libgit2.h"
+#include "git2/sys/email.h"
 
 #include "diff_generate.h"