ANDROID: GKI: remove CONFIG_CMDLINE_EXTEND from arm64 gki_defconfig

In commit cae118b6 ("arm64: Drop support for CMDLINE_EXTEND"), this
configuration option was removed, so also remove it from the arm64
gki_defconfig so that the build continues to work properly.

Fixes: cae118b6 ("arm64: Drop support for CMDLINE_EXTEND")
Cc: Will Deacon <willdeacon@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1d6570e840134efc62d7c9ab4a25b63725999e0d