Remove setting of GOMODULE env var in Dockerfiles

[DimitrisJim]

Description

appears to have been a typo of GO111MODULE, locally has no effect once removed.

ref #4532 (comment)

closes: #XXXX

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[damiannolan]

Nice nice! I think its no longer needed because of updates to Go

[DimitrisJim]

think its no longer needed because of updates to Go

yea, tho I'm pretty sure that's GO111MODULE which this env var was hoping to be 😄

[chatton]

LGTM! Thanks for the cleanup