Remove the border-left from the toolbar

[hypest]

Fixes #639

Gutenberg side PR: WordPress/gutenberg#20881

With the left border	Without the left border

To test:

1. Run the demo app and capture a screenshot of the app
2. Notice that there is no 1-pixel grey border to the left of the Inserter button

cc @iamthomasbishop in case you also want to try this out.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[marecar3]

We're freezing 1.24.0 today. If you think it is ready and if you'd like to ship it with 1.24.0please merge it into develop branch. Otherwise, we can bump it to 1.25.0. @hypest @cameronvoell

[hypest]

Moved to 1.25, although this PR will probably get closed in favor of #2004

[SergioEstevao]

@hypest I'm moving this to 1.26, feel free to move it back to 1.25 if this is something that can be considered a regression.

[pinarol]

I am changing the milestone of this PR as 1.27 because the 1.26 release branch will be cut quite soon. Let me know if you instead wanted to include this to 1.26.

[mkevins]

Hi @hypest wave smiley since this one is still awaiting review (and will possibly be superseded), I'll bump the milestone to 1.28. Please let me know if you wanted to get this into the 1.27 release.

[SergioEstevao]

@hypest do you still want to have this on 1.28 ?

[SergioEstevao]

I think this other PR solved the original issue.

Do you want to close this one @hypest ?

[hypest]

Will close this one to remove the confusion. Was waiting for #2004 to land first before closing but yeah, no real need to postpone.