Remove dependency of System.Collections (#13)

***NO_CI***

System.IO.Ports/SerialDeviceEventListener.cs

@@ -4,7 +4,6 @@
 //
 
 using nanoFramework.Runtime.Events;
-using System;
 using System.Collections;
 
 namespace System.IO.Ports
@@ -87,6 +86,5 @@ namespace System.IO.Ports
 
             return null;
         }
-
     }
 }

System.IO.Ports/System.IO.Ports.nfproj

@@ -73,10 +73,6 @@
       <HintPath>..\packages\nanoFramework.Runtime.Events.1.9.1-preview.5\lib\nanoFramework.Runtime.Events.dll</HintPath>
       <Private>True</Private>
     </Reference>
-    <Reference Include="nanoFramework.System.Collections, Version=1.2.0.0, Culture=neutral, PublicKeyToken=c07d481e9758c731">
-      <HintPath>..\packages\nanoFramework.System.Collections.1.2.0-preview.67\lib\nanoFramework.System.Collections.dll</HintPath>
-      <Private>True</Private>
-    </Reference>
     <Reference Include="nanoFramework.System.Text, Version=1.1.1.0, Culture=neutral, PublicKeyToken=c07d481e9758c731">
       <HintPath>..\packages\nanoFramework.System.Text.1.1.1-preview.61\lib\nanoFramework.System.Text.dll</HintPath>
       <Private>True</Private>
@@ -95,4 +91,4 @@
     </PropertyGroup>
     <Error Condition="!Exists('..\packages\Nerdbank.GitVersioning.3.4.194\build\Nerdbank.GitVersioning.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Nerdbank.GitVersioning.3.4.194\build\Nerdbank.GitVersioning.targets'))" />
   </Target>
-</Project>
+</Project>

System.IO.Ports/packages.config

@@ -2,7 +2,6 @@
 <packages>
   <package id="nanoFramework.CoreLibrary" version="1.10.5-preview.13" targetFramework="netnanoframework10" />
   <package id="nanoFramework.Runtime.Events" version="1.9.1-preview.5" targetFramework="netnanoframework10" />
-  <package id="nanoFramework.System.Collections" version="1.2.0-preview.67" targetFramework="netnanoframework10" />
   <package id="nanoFramework.System.Text" version="1.1.1-preview.61" targetFramework="netnanoframework10" />
   <package id="Nerdbank.GitVersioning" version="3.4.194" developmentDependency="true" targetFramework="netnanoframework10" />
 </packages>

nanoFramework.System.IO.Ports.nuspec

@@ -21,7 +21,6 @@
     <dependencies>
       <dependency id="nanoFramework.CoreLibrary" version="1.10.5-preview.13" />
       <dependency id="nanoFramework.Runtime.Events" version="1.9.1-preview.5" />
-      <dependency id="nanoFramework.System.Collections" version="1.2.0-preview.67" />
       <dependency id="nanoFramework.System.Text" version="1.1.1-preview.61" />
     </dependencies>
   </metadata>