Removed unadvertised ACL2(h)-only declare forms dynamic-extent, inline, and notinline.

Quoting :doc note-7-0:

  We removed support for three [declare] forms that had been permitted
  in ACL2(h) only, but were not advertised: dynamic-extent, inline
  and notinline, because they seem difficult or impossible to support
  correctly. For alternatives to using inline and notinline
  declarations, see [defun-inline] and [defun-notinline].
Merge pull request #320 from nadezhin/master

typo in arithmetic/natp-posp.lisp

Thanks for the fix and pull-request Dmitry!