Two stars. Rated R. 100 minutes. “Equity,” a drama about female executives navigating sexism on Wall Street, has received lots of attention for being a movie written, directed, produced by and starring women. As an example of doing-it-for-ourselves solidarity and self reliance, it’s unquestionably inspiring: a bracing example of the old admonition to organize rather than sit around complaining. The aspirations of “Equity” are so admirable that it’s all the more disappointing that the film itself is a letdown.