Remove some unnecessary duplicatioN

remove checks for failure after memory allocation calls that cannot fail:

kmem_alloc() with KM_SLEEP
kmem_zalloc() with KM_SLEEP
percpu_alloc()
pserialize_create()
psref_class_create()

al

remove checks for failure after memory allocation calls that cannot fail:

kmem_alloc() with KM_SLEEP
kmem_zalloc() with KM_SLEEP
percpu_alloc()
pserialize_create()
psref_class_create()

all of these paths include an assertion that the allocation has not failed,
so callers should not assert that again.

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Remove the 'cred' argument from bread(). Remove a now unused var in
ffs_snapshot.c. Update the man page accordingly.

ok hannken@

v7fs: replace malloc(9) with kmem(9), fix a memory leak and few missing
mutex destruction cases in the error path.

7th Edition(V7) File System support. and NetBSD symbolic-link, socket, FIFO extension. see newfs_v7fs(8).