[build] Remove WearOS emulator CI lane

[jonathanpeppers]

Context: #11203 (comment)

Summary

Remove the wear_tests job from stage-msbuild-emulator-tests.yaml and the
now-unused [Category ("WearOS")] attributes from the two test methods that
referenced it.

Rationale

The WearOS CI lane spins up 2 parallel macOS agents with an x86 API 30
wear_square emulator (180-minute timeout each) to run just 2 test
methods:

Test	File	What it actually tests
ApplicationRunsWithDebuggerAndBreaks	DebuggingTest.cs	Generic debugger attach/break -- not WearOS-specific
DotNetInstallAndRunPreviousSdk	InstallAndRunTests.cs	Generic install + run with previous SDK -- not WearOS-specific

Neither test exercises any WearOS API, layout, or behavior. They are standard
app tests that happen to be re-run on a Wear emulator.

These tests already run in the main MSBuild+Emulator lane. The main lane's
filter (cat != SystemApplication & cat != TimeZoneInfo & cat != Localization)
does not exclude the WearOS category, so both tests execute there too.

What is preserved

• WearTests.cs -- 3 MSBuild-level build tests (BasicProject,
  BundledWearApp, WearProjectJavaBuildFailure) that validate WearOS project
  builds without needing an emulator.
• android-wear template -- the dotnet new androidwear template and all
  its localization files are untouched.
• XamarinAndroidWearApplicationProject -- test infrastructure class remains
  for use by the build-only tests.

What is removed

• The wear_tests job (x86 API 30 android-wear emulator, 2 agents)
• [Category ("WearOS")] from DebuggingTest.ApplicationRunsWithDebuggerAndBreaks
• [Category ("WearOS")] from InstallAndRunTests.DotNetInstallAndRunPreviousSdk

Cost/benefit

	Before	After
macOS agent-minutes per PR	2 x 180 min (WearOS) + main lane	main lane only
Unique test coverage from WearOS lane	None -- tests are not WearOS-specific	Same tests run in main lane
WearOS build validation	WearTests.cs (3 tests)	WearTests.cs (3 tests) -- unchanged
Flakiness from x86 API 30 Wear emulator	Frequent failures	Eliminated

[Copilot]

Pull request overview

This PR removes the dedicated WearOS emulator CI job and drops the now-unused NUnit WearOS category from the two test methods that were only used to route tests into that lane.

Changes:

• Removed the wear_tests job from build-tools/automation/yaml-templates/stage-msbuild-emulator-tests.yaml.
• Removed [Category ("WearOS")] from ApplicationRunsWithDebuggerAndBreaks in DebuggingTest.cs.
• Removed [Category ("WearOS")] from DotNetInstallAndRunPreviousSdk in InstallAndRunTests.cs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
build-tools/automation/yaml-templates/stage-msbuild-emulator-tests.yaml	Deletes the WearOS emulator CI lane/job and its steps.
tests/MSBuildDeviceIntegration/Tests/DebuggingTest.cs	Removes WearOS-only test categorization while keeping the Debugger categorization.
tests/MSBuildDeviceIntegration/Tests/InstallAndRunTests.cs	Removes WearOS-only test categorization from the previous-SDK install/run test.