Remove IsPreRelease msbuild property (#72169)

* Remove IsPreRelease msbuild property

The property was added in dotnet/coreclr@809b8f7 years ago and isn't used anymore. Remove it to ease branding.

* Update configureplatform.cmake

Author: ViktorHofer

Directory.Build.props

@@ -277,9 +277,6 @@
     <Copyright>$(CopyrightNetFoundation)</Copyright>
     <PackageThirdPartyNoticesFile>$(MSBuildThisFileDirectory)THIRD-PARTY-NOTICES.TXT</PackageThirdPartyNoticesFile>
     <PackageReleaseNotes>https://go.microsoft.com/fwlink/?LinkID=799421</PackageReleaseNotes>
-    <!-- Indicates this is not an officially supported release. Release branches should set this to false. -->
-    <!-- Keep it in sync with PRERELEASE in eng/native/configureplatform.cmake -->
-    <IsPrerelease>false</IsPrerelease>
     <IsPrivateAssembly>$(MSBuildProjectName.Contains('Private'))</IsPrivateAssembly>
     <!-- Private packages should not be stable -->
     <SuppressFinalPackageVersion Condition="'$(SuppressFinalPackageVersion)' == '' and $(IsPrivateAssembly)">true</SuppressFinalPackageVersion>

eng/native/configureplatform.cmake

@@ -1,8 +1,8 @@
 include(${CMAKE_CURRENT_LIST_DIR}/functions.cmake)
 
-# If set, indicates that this is not an officially supported release
-# Keep in sync with IsPrerelease in Directory.Build.props
-set(PRERELEASE 0)
+# If set, indicates that this is not an officially supported release.
+# Release branches should set this to false.
+set(PRERELEASE 1)
 
 #----------------------------------------
 # Detect and set platform variable names