Revert "dashboard/config/linux: disable -Werror on clang instances"
Revert "dashboard/config/linux: disable -Werror on clang instances"

This reverts commit e096c0a2a414e487412c9669426780ce5acdde9d.

After a long discussion [1], Linus decided to default WERROR to
COMPILE_TEST [2]. This means we no longer have to unset the option
explicitly.

[1] https://lkml.kernel.org/r/YTfkO2PdnBXQXvsm@elver.google.com
[2] https://git.kernel.org/torvalds/c/b339ec9c229aaf399296a120d7be0e34fbc355ca

google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller