Background rocket fix

[afonit]

Taking a stab at removing the backgrounds of the two icons mentioned here:
#6624

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[ellisonbg]

Sorry about the mis-communication. I ended up doing a huge refactor of icons in #6664 and we ended up moving away from the rocket icon altogether, in favor of a Material Design icon (its launch one):

https://material.io/tools/icons/?search=launch&style=baseline

There were two reasons for this: 1) we don't know where the rocket came from, and are a bit unsure about its license - especially as we modify it 2) we want to maintain as few custom icons as possible, so if there is one from MD that will work, we want to use it.

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