Remove Kernel#caller patches

[wied03]

Karma-opal-rspec is now using stacktrace.js:

This issue should now:

• Remove the Kernel#caller override in opal-rspec and just put in pure, raw JS stack traces only when a test fails and point people elsewhere (wherever this github issue gets done) to use source maps. Better yet, don't include any location info to avoid the overhead (see next bullet)
• Compiler/Line Number Metadata #57 might be a more performant way of gathering metadata for every test

[wied03]

@elia - Do you think this belongs in a separate GEM? These Bower dependencies can be pulled in via rails-assets (I use that to represent Bower deps as GEMs on my project) but I think this probably belongs in a separate GEM.

[elia]

@wied03 I'm quite sure this should be optional, not necessarily by using another gem but one shouldn't be forced in. Although an argument in favor of an external gem can be made by pointing out that the gem could be independent from RSpec and just provide source-mapped backtraces to opal on nodejs.

[wied03]

Some Kernel#caller discussion here - opal/opal#894