Xavier Thompson reports that when Theia is compiled inside Theia, Go fails to install with the error showing that golang14's make.bash calls go install to install cmd/go and other commands to the outer go.work/bin instead of inside $GOROOT_FINAL set by the build recipe.

Similarly to !928 (merged) this might be to the fact that internal go install prioritizes $GOBIN even in the presence of set $GOROOT_FINAL.

-> Don't try to fix Go itself, and make the compilation more robust by unsetting $GOBIN, so that even if that variable is set in the environment where buildout runs, it does not affect the compilation procedure.

Fixes: 8eac67a5 (golang: Prepare for future GOPATH removal)
Reported-on: https://www.erp5.com/group_section/forum/Go-compilation-error-P6f5WisQkc

/cc @xavier_thompson, @jerome