extensions: refactor function for obtaining disabled extension help The way this worked before was hgext.__index__ was consulted. This file appears to only be present on some Windows distributions. This file contains a dict mapping extension name to its summary line, not its full docstring. The problem with this is that code in the help system was calling this function to resolve help text. If hgext.__index__ was present, only the summary line would be displayed. If not, the full extension help would be printed. This commit changes the function to not use hgext.__index__ such that it always returns the full extension help text. As a result of this change, test-extension.t and test-qrecord.t now pass when run from environments that have an hgext.__index__. Differential Revision: https://phab.mercurial-scm.org/D8344