git_mwindow_file_deregister() shouldn't return errors

As a function that appears to only be called on error paths, I don't
think it makes sense for it to return an error, or clobber the global
giterr. Note that no existing callsites actually check the return
code.

In my own application, there are errors where the real error ends
up being hidden, as git_mwindow_file_deregister() clobbers the
global giterr. I'm not sure this error is even relevant?

src/mwindow.c

@@ -293,28 +293,23 @@ int git_mwindow_file_register(git_mwindow_file *mwf)
 	return ret;
 }
 
-int git_mwindow_file_deregister(git_mwindow_file *mwf)
+void git_mwindow_file_deregister(git_mwindow_file *mwf)
 {
 	git_mwindow_ctl *ctl = &mem_ctl;
 	git_mwindow_file *cur;
 	unsigned int i;
 
-	if (git_mutex_lock(&git__mwindow_mutex)) {
-		giterr_set(GITERR_THREAD, "unable to lock mwindow mutex");
-		return -1;
-	}
+	if (git_mutex_lock(&git__mwindow_mutex))
+		return;
 
 	git_vector_foreach(&ctl->windowfiles, i, cur) {
 		if (cur == mwf) {
 			git_vector_remove(&ctl->windowfiles, i);
 			git_mutex_unlock(&git__mwindow_mutex);
-			return 0;
+			return;
 		}
 	}
 	git_mutex_unlock(&git__mwindow_mutex);
-
-	giterr_set(GITERR_ODB, "Failed to find the memory window file to deregister");
-	return -1;
 }
 
 void git_mwindow_close(git_mwindow **window)

src/mwindow.h

@@ -39,7 +39,7 @@ int git_mwindow_contains(git_mwindow *win, git_off_t offset);
 void git_mwindow_free_all(git_mwindow_file *mwf);
 unsigned char *git_mwindow_open(git_mwindow_file *mwf, git_mwindow **cursor, git_off_t offset, size_t extra, unsigned int *left);
 int git_mwindow_file_register(git_mwindow_file *mwf);
-int git_mwindow_file_deregister(git_mwindow_file *mwf);
+void git_mwindow_file_deregister(git_mwindow_file *mwf);
 void git_mwindow_close(git_mwindow **w_cursor);
 
 #endif