Remove Pester and platyPS as build dependencies (#54)

Pester and platyPS are already installed and loaded on GH Actions.
Trying to load them again raises an error because the assemblies
are already loaded.

Author: devblackops

requirements.psd1

@@ -1,21 +1,10 @@
 @{
-    PSDependOptions = @{
+    PSDependOptions  = @{
         Target = 'CurrentUser'
     }
-    BuildHelpers = @{
-        Version = '2.0.16'
-    }
-    Pester = @{
-        Parameters = @{
-            MinimumVersion = '5.3.0'
-            SkipPublisherCheck = $true
-        }
-    }
-    platyPS = '0.14.1'
-    PowerHtml = 'latest'
-    PowerShellBuild = @{
-        RequiredVersion = '0.6.1'
-    }
-    psake = '4.9.0'
+    BuildHelpers     = '2.0.16'
+    PowerHtml        = 'latest'
+    PowerShellBuild  = '0.6.1'
+    psake            = '4.9.0'
     PSScriptAnalyzer = '1.19.1'
 }