remove unnecessary Update verb

Author: brettfo

src/fsharp/FSharp.Build/Microsoft.FSharp.Targets

@@ -432,24 +432,21 @@ this file.
 
       <ItemGroup>
         <!-- Update references to `.NETCore\*\FSharp.Core.dll`. -->
-        <Reference Update="%(Reference.Identity)"
-                   Condition="'%(Reference.Identity)' == 'FSharp.Core' and
+        <Reference Condition="'%(Reference.Identity)' == 'FSharp.Core' and
                               '%(Reference.HintPath)' == '$(_OldCoreSdkPath)' and
                               Exists('$(_NewCoreSdkPath)')">
           <HintPath>$(_NewCoreSdkPath)</HintPath>
         </Reference>
 
         <!-- Update references to `.NETFramework\v4.0\*\FSharp.Core.dll`. -->
-        <Reference Update="%(Reference.Identity)"
-                   Condition="'%(Reference.Identity)' == 'FSharp.Core' and
+        <Reference Condition="'%(Reference.Identity)' == 'FSharp.Core' and
                               '%(Reference.HintPath)' == '$(_OldFrameworkSdkPath)' and
                               Exists('$(_NewFrameworkSdkPath)')">
           <HintPath>$(_NewFrameworkSdkPath)</HintPath>
         </Reference>
 
         <!-- Update references to `.Portable\*\FSharp.Core.dll`. -->
-        <Reference Update="%(Reference.Identity)"
-                   Condition="'%(Reference.Identity)' == 'FSharp.Core' and
+        <Reference Condition="'%(Reference.Identity)' == 'FSharp.Core' and
                               '%(Reference.HintPath)' == '$(_OldPortableSdkPath)' and
                               Exists('$(_NewPortableSdkPath)')">
           <HintPath>$(_NewPortableSdkPath)</HintPath>