Rename read_ubyte_unaligned_inc to read_addr_unaligned_inc

Rename read_ubyte_unaligned_inc to read_addr_unaligned_inc

- The behavior of this function has been changed to read only
  address-sized quantities, i.e. the size of 2 is no longer allowed.
  (Size of 1 never was.)  The two outstanding uses, both in readelf.c,
  which actually do use this call to read address-sized units, were
  updated, rejecting fields that indicate weird address sizes.

- The three related calls, read_sbyte_unaligned_inc,
  read_ubyte_unaligned and read_sbyte_unaligned were dropped.  There
  are currently no uses for these calls.

Signed-off-by: Petr Machata <pmachata@redhat.com>