hack: remove deprecated export GO111MODULE=on from shell scripts

[Ankitsinghsisodya]

Problem

Several scripts set export GO111MODULE=on:

• hack/verify-codegen.sh line 21
• hack/e2e-debug.sh line 17
• test/e2e-common.sh line 21

GO111MODULE was a Go 1.11 feature flag to opt into modules. Since Go 1.16 modules are on by default, and since Go 1.21 the variable is completely ignored. This repository's go.mod already declares go 1.25.0, so the export is dead code.

Proposed Fix

Remove all export GO111MODULE=on lines from the scripts listed above.

[Ankitsinghsisodya]

/assign