Drop a redundant binary entry size assignment

By definition, the length of a regular binary type entry equals it's count
so this is just redundant. The key word being regular, regions are a
different matter entirely: the assignment was originally introduced around
the turn of millenium in commit db32ab6bea,
apparently to include alignment in header region count but the surrounding
code has changed significantly since then...

Thanks to Michael Schroeder for pointing this out (in #308)

lib/header.c

@@ -1105,7 +1105,6 @@ static int copyTdEntry(const indexEntry entry, rpmtd td, headerGetFlags flags)
 	    /* XXX 1 on success. */
 	    rc = (rc < 0) ? 0 : 1;
 	} else {
-	    count = entry->length;
 	    td->data = (!minMem
 		? memcpy(xmalloc(count), entry->data, count)
 		: entry->data);