Run Test-Path before Remove-Item to prevent Health Checker exception

[lusassl-msft]

Issue:
Health Checkers makes use of the new Test-ScriptVersion function. In case an update is processed we're trying to remove an existing HealthChecker.ps1 and HealthChecker.old file which may be there caused by previous update. In case there is no HealthChecker.ps1 in Temp and/or no HealthChecker.old we run into an error on HealthChecker (caused by how we handle errors in the script). We show the following:

Reason:
This is caused by the Remove-Item call against a non-existing HealthChecker.ps1 and/or non-existing HealthChecker.old files (update never happend before).

[DBG]: PS C:\Users\administrator.EXCHANGELABS\Desktop\hc>> $error[0]
Remove-Item : Cannot find path 'C:\Users\ADMINI~1.EXC\AppData\Local\Temp\HealthChecker.ps1' because it does not exist.
At C:\Users\administrator.EXCHANGELABS\Desktop\hc\HealthChecker.ps1:255 char:17
+ ...             Remove-Item $tempFullName -Force -Confirm:$false -ErrorAc ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:\Users\ADMINI...althChecker.ps1:String) [Remove-Item], ItemNotFoundException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.PowerShell.Commands.RemoveItemCommand

Fix:
This can be easily avoided by running Test-Path before Remove-Item.

Validation:
Validated in Lab. Possible Pester test case.