ShellPkg AARCH64: remove DEBUG BuildOptions override

ShellPkg AARCH64: remove DEBUG BuildOptions override

The BuildOptions for AARCH64 in Application/Shell/Shell.inf only affect
the core Shell binary, and not the Shell component libraries which are
merged into the final Shell binary via NULL library class resolution.

This means we need to override the UEFI_APPLICATION build options in
the platform .DSC anyway, there is no point in setting these options
here as well. So remove them.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>