ATLASMagneticFieldWrapper: remove workaround for copy
This removes a workaround for AtlasFieldCache
not being copyable, that I added in !68255 (merged), but is not needed anymore after !68215 (merged)
This removes a workaround for AtlasFieldCache
not being copyable, that I added in !68255 (merged), but is not needed anymore after !68215 (merged)