Remove unnecessary options from fast-import.

Remove unnecessary options from fast-import.

The --objects command line option is rather unnecessary.  Internally
we allocate objects in 5000 unit blocks, ensuring that any sort
of malloc overhead is ammortized over the individual objects to
almost nothing.  Since most frontends don't know how many objects
they will need for a given import run (and its hard for them to
predict without just doing the run) we probably won't see anyone
using --objects.  Further since there's really no major benefit
to using the option, most frontends won't even bother supplying
it even if they could estimate the number of objects.  So I'm
removing it.

The --max-objects-per-pack option was probably a mistake to even
have added in the first place.  The packfile format is limited
to 4 GiB today; given that objects need at least 3 bytes of data
(and probably need even more) there's no way we are going to exceed
the limit of 1<<32-1 objects before we reach the file size limit.
So I'm removing it (to slightly reduce the complexity of the code)
before anyone gets any wise ideas and tries to use it.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>