[strip.sh] Move remaining GNU binutils usage to llvm binutils

With clang r377782, llvm binutils implements all the necessary
funtionaility for strip.sh. We can finally get rid of all the fallback
GNU binutils usage.

Test: m
Bug: 141010852
Bug: 135627985
Change-Id: I110f6028dab7f599decf59a5cb1b927b35e11857