ice: avoid unnecessary single-member variable-length structs

There are a number of structures that consist of a one-element array as the
only struct member.  Some of those are unused so remove them. Others are
used to index into a buffer/array consisting of a variable number of a
different data or structure type.  Those are unnecessary since we can use
simple pointer arithmetic or index directly into the buffer to access
individual elements of the buffer/array.

Additional code cleanups were done near areas affected by this change.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>