(chocolatey#3364) Remove ounusable tab completion tests

These tests are verifying the old method and are targeting an
implementation detail, rather than actually checking the tab completion
results, which the following tests do anyway.

As such, we're best off removingthem as there is no direct way to check
the same things for the Register-ArgumentCompleter method. The tests for
the tab completion results themselves covers this adequately already.

tests/pester-tests/chocolateyProfile.Tests.ps1

@@ -11,14 +11,6 @@ Describe "Chocolatey Profile" -Tag Chocolatey, Profile, Environment {
     }
 
     Context "Tab Completion" {
-        It "Should Exist" {
-            Test-Path Function:\TabExpansion | Should -BeTrue
-        }
-
-        It "Should have overridden TabExpansion with a new scriptblock including ChocolateyTabExpansion" {
-            [bool]((Get-Command TabExpansion).ScriptBlock -match "ChocolateyTabExpansion") | Should -BeTrue
-        }
-
         It "Should list completions for all Top Level Commands, sorted alphabetically, but not aliases or unpackself" {
             $Command = "choco "
             $Completions = (TabExpansion2 -inputScript $Command -cursorColumn $Command.Length).CompletionMatches.CompletionText