`orgtbl-to-generic' speed-up

`orgtbl-to-generic' speed-up

* lisp/org-element.el (org-element-class): Make it a defsubst.
* lisp/org-table.el (orgtbl-to-generic): Do not use cache when
  building Org table.  Factor out calls to Org Export functions when
  they are not necessary.
(org-table--to-generic-row): Factor out calls to Org Export functions
when they are not necessary.
* lisp/ox.el (org-export-resolve-fuzzy-link):
(org-export-table-has-header-p):
(org-export-table-row-group):
(org-export-table-cell-width):
(org-export-table-cell-alignment): Small refactoring.
(org-export-table-row-number): Add caching.

* testing/lisp/test-org-element.el (test-org-element/class): Remove
  test.