There is a way, but involves private API.
Sometimes Apple makes exceptions, especially if you fix a bug.
Let's dive into details...
UIActivityViewController has got a private method called "_availableActivitiesForItems:", which returns an array of UISocialActivity objects.
UISocialActivity has got an interesting property, called "activityType", which returns a domain-formatted activity type.
After some tests, I managed to discover the Reminder and Notes activity types:
- com.apple.reminders.RemindersEditorExtension
- com.apple.mobilenotes.SharingExtension
Unfortunately, passing those two types into ".excludedActivityTypes" didn't make any difference.
"_availableActivitiesForItems:" to the rescue!
OLD WAY:
Update: I've found a better way to do it.
The first solution I've posted doesn't work in some cases, thus shouldn't be considered stable.
Header:
#import <UIKit/UIKit.h>
@interface UISocialActivity : NSObject
- (id)activityType;
@end
@interface UIActivityViewController (Private)
- (id)_availableActivitiesForItems:(id)arg1;
@end
@interface ActivityViewController : UIActivityViewController
@end
Implementation:
@implementation ActivityViewController
- (id)_availableActivitiesForItems:(id)arg1
{
    id activities = [super _availableActivitiesForItems:arg1];
    NSMutableArray *filteredActivities = [NSMutableArray array];
    [activities enumerateObjectsUsingBlock:^(UISocialActivity*  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        if (![[obj activityType] isEqualToString:@"com.apple.reminders.RemindersEditorExtension"] &&
            ![[obj activityType] isEqualToString:@"com.apple.mobilenotes.SharingExtension"]) {
            [filteredActivities addObject:obj];
        }
    }];
    return [NSArray arrayWithArray:filteredActivities];
    }
    @end
NEW WAY:
Header:
@interface UIActivityViewController (Private)
- (BOOL)_shouldExcludeActivityType:(UIActivity*)activity;
@end
@interface ActivityViewController : UIActivityViewController
@end
Implementation:
@implementation ActivityViewController
- (BOOL)_shouldExcludeActivityType:(UIActivity *)activity
{
    if ([[activity activityType] isEqualToString:@"com.apple.reminders.RemindersEditorExtension"] ||
        [[activity activityType] isEqualToString:@"com.apple.mobilenotes.SharingExtension"]) {
        return YES;
    }
    return [super _shouldExcludeActivityType:activity];
}
@end
"Illegal", but it works.
It would be great to know if it actually passes Apple validation.