common sizeArray: remove platform-conditional struct code

common sizeArray: remove platform-conditional struct code

08f481fa36bbf199e0f8fbf862639d8fc4e575ab made this initialization platform
dependent and its commit message does not explain why. Both statements are
equivalent; the value of `Agstrictdirected` _is_ `{ 1, 1, 0, 1 }`. This change
removes the Windows branch of this which was causing warnings under MinGW
12.2.0:

  lib/common/htmltable.c:1472:5: error: missing initializer for field 'flatlock'
    of 'Agdesc_t' {aka 'struct Agdesc_s'} [-Werror=missing-field-initializers]
   1472 |     Agdesc_t dir = { 1, 1, 0, 1 };
        |     ^~~~~~~~
  In file included from lib/common/types.h:41,
                   from lib/common/render.h:29,
                   from lib/common/htmltable.c:32:
  lib/cgraph/cgraph.h:166:14: note: 'flatlock' declared here
    166 |     unsigned flatlock:1;        /* if sets are flattened into lists…
        |              ^~~~~~~~