any ideas how to remove these without the key in the bottom corner

Mole grips or an angle grinder.

Mole grips on which end???

Screw extractor?  I’d need to see an end shot. 

I’m sure I used to have these, are they a pentagonal key?

I’d need to see an end shot.

I think they’re a kind of five sided hex bolt.

I’d go with some grips on the “nut” end.

I’ve looked now.
If you can squeeze the black outer on to the pentagonal socket bolt mole grips will probably work, but check the black outer doesn’t have a texture against the drop out that might mangle the drop out a little (don’t know how you check).
But given I have screw extractors and they’d drop into that pentagonal socket that’s the minimum damage route I suspect.

Torx may help. 

https://www.google.com/aclk?sa=L&ai=DChcSEwjaqLWu2NSCAxUayO0KHRARB5QYABAKGgJkZw&gclid=EAIaIQobChMI2qi1rtjUggMVGsjtCh0QEQeUEAQYASABEgLuY_D_BwE&sph=&sig=AOD64_1QorFgLJ-L-9fPwm927tjDwy_XJw&ctype=5&q=&ved=2ahUKEwjt2bCu2NSCAxXXQkEAHdYTDGg4ChDCDygAegQIABAM&nis=8&adurl=

Pentagon keys any good?

Buy a new key for £3.99

https://www.sjscycles.co.uk/hub-spares/transx-replacement-special-key-for-antitheft-sets/

I had similar on a bike that was given to me, managed to wedge a torx key into the bit on the right hand side of that photo and just unscrewed it.

A bike shops answer was to ram a torx or allen key in

Sorted, knipex pliers on the nut end