Removing ARM based tests as this is not supported yet (#443)

# Preface

Please ensure you have read the [contribution
docs](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md) prior
to submitting the pull request. In particular,
[pull request
guidelines](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md#pull-request-best-practices).

## Description

This change removed the AARCH64 support for the host based unit tests
for PolicyServicesPkg because this is not yet supported.

Removing the support in this DSC file to fix the broken pipeline build
on AARCH64 systems.

For each item, place an "x" in between `[` and `]` if true. Example:
`[x]`.
_(you can also check items in the GitHub UI)_

- [x] Impacts functionality?
- **Functionality** - Does the change ultimately impact how firmware
functions?
- Examples: Add a new library, publish a new PPI, update an algorithm,
...
- [ ] Impacts security?
- **Security** - Does the change have a direct security impact on an
application,
    flow, or firmware?
  - Examples: Crypto algorithm change, buffer overflow fix, parameter
    validation improvement, ...
- [ ] Breaking change?
- **Breaking change** - Will anyone consuming this change experience a
break
    in build or boot behavior?
- Examples: Add a new library class, move a module to a different repo,
call
    a function in a new library class in a pre-existing module, ...
- [ ] Includes tests?
  - **Tests** - Does the change include any explicit test code?
  - Examples: Unit tests, integration tests, robot tests, ...
- [ ] Includes documentation?
- **Documentation** - Does the change contain explicit documentation
additions
    outside direct code modifications (and comments)?
- Examples: Update readme file, add feature readme file, link to
documentation
    on an a separate Web page, ...

## How This Was Tested

N/A

## Integration Instructions

N/A

PolicyServicePkg/Test/PolicyServicePkgHostTest.dsc

@@ -12,7 +12,7 @@
   PLATFORM_VERSION        = 0.1
   DSC_SPECIFICATION       = 0x00010005
   OUTPUT_DIRECTORY        = Build/PolicyServicePkg/HostTest
-  SUPPORTED_ARCHITECTURES = IA32|X64|AARCH64
+  SUPPORTED_ARCHITECTURES = IA32|X64
   BUILD_TARGETS           = NOOPT
   SKUID_IDENTIFIER        = DEFAULT