Fix: Use default assertion messages for rule tester messages

[aaronabramov]

Fixes #6532

[eslintbot]

Thanks for the pull request, @DmitriiAbramov! I took a look to make sure it's ready for merging and found some changes are needed:

• The commit summary must be 72 characters or shorter. Please check out our guide for how to properly format your commit summary and update it on this pull request.

Can you please update the pull request to address these?

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[eslintbot]

LGTM

[ilyavolodin]

I wonder if we want to do the same for everything (type, line, column, etc.)

[platinumazure]

Hmm. This might just need a force-push to restart the Travis build.

I agree with @ilyavolodin about removing messages from all assertions, if feasible.

[aaronabramov]

yeah. i'll update the PR

[nzakas]

Let's not expand the scope of this PR further than it was originally intended.

@ilyavolodin if you want to propose other changes, please open a separate issue as I have concerns about removing the message for other assertions.

[ilyavolodin]

@nzakas Ok, sounds good. Should we merge this in as is than?

[nzakas]

Yeah. I just realized the Travis failure was the Node 6 thing we already fixed. LGTM.