doc: fix inconsistent spelling of "packfile"

Fix remaining instances where "pack-file" is used instead of
"packfile". Some places remain where we still use "pack-file",
This is the case when we explicitly refer to a file with a
".pack" extension as opposed to a data source providing a pack
data stream.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-unpack-objects.txt

@@ -9,7 +9,7 @@ git-unpack-objects - Unpack objects from a packed archive
 SYNOPSIS
 --------
 [verse]
-'git unpack-objects' [-n] [-q] [-r] [--strict] < <pack-file>
+'git unpack-objects' [-n] [-q] [-r] [--strict] < <packfile>
 
 
 DESCRIPTION

Documentation/technical/pack-protocol.txt

@@ -465,7 +465,7 @@ contain all the objects that the server will need to complete the new
 references.
 
 ----
-  update-request    =  *shallow ( command-list | push-cert ) [pack-file]
+  update-request    =  *shallow ( command-list | push-cert ) [packfile]
 
   shallow           =  PKT-LINE("shallow" SP obj-id LF)
 
@@ -491,7 +491,7 @@ references.
 		      *PKT-LINE(gpg-signature-lines LF)
 		      PKT-LINE("push-cert-end" LF)
 
-  pack-file         = "PACK" 28*(OCTET)
+  packfile          = "PACK" 28*(OCTET)
 ----
 
 If the receiving end does not support delete-refs, the sending end MUST