Add objectWithoutPropertiesLoose to generate-helpers.js

[RobMaskell]

The babel helper objectWithoutProperties calls objectWithoutPropertiesLoose which needs to be included in generate-helpers.js in the build package in order to avoid an error.
I found this while testing with "@babel/core": "^7.2.2" which fixes an issue I had with rest/spread operators not working in the version of babel used by polymer.

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[RobMaskell]

I signed it!

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CLAs look good, thanks!

[RobMaskell]

Doesn't look like the build failure is anything to do with my change, seems to be expecting Chrome 69+ but getting 62

[RobMaskell]

Might be related to this 2f10194

[RobMaskell]

@aomarks does this need to be released on it's own of does it get sucked by something else?

[armujahid]

It's strange but I am still getting this error in IE from code compiled using latest polymer cli v1.9.11
Object doesn't support property or method 'objectWithoutPropertiesLoose'
I can see that generate helper file has objectWithoutPropertiesLoose so I am not sure what's the root cause.

tools/packages/build/scripts/generate-helpers.js

Line 76 in 1fe1c22

'objectWithoutPropertiesLoose',