[CrOS Cellular] Remove strayed function definition in euicc.h

This CL simply removes the strayed function definition in euicc.h.

Change-Id: Iabc05d5ffd374cbde7bf27cf84b0f6597052173e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3390732


Reviewed-by: Azeem Arshad <azeemarshad@chromium.org>
Commit-Queue: Jason Zhang <jiajunz@google.com>
Cr-Commit-Position: refs/heads/main@{#963086}