sys/vfs/hammer: Drop typedefs for struct hammer_ioc_{hist_entry,mrecord_head}

sys/vfs/hammer: Drop typedefs for struct hammer_ioc_{hist_entry,mrecord_head}

These are the only two ioctl structs with pointer typedefs. All the
rest of ioctl structs aren't typedef'd, and there isn't really any
reason that these two need to be typedef'd.

Note that almost all non ioctl HAMMER structs have pointer typedef,
and majority of variables have been typedef'd ones from the beginning
(since they were mostly pointers). Rest were changed to use typedef'd
at some point in 2016, to avoid mix of these for no reason, though
typedef'd pointers have ugliness when used as const.