Bump version to 2.44.0 (on v2.44.x branch) (#1640)

Author: jtattermusch

build/version.props

@@ -2,7 +2,7 @@
   <PropertyGroup>
 
     <!-- package version of grpc-dotnet -->
-    <GrpcDotnetVersion>2.44.0-pre1</GrpcDotnetVersion>
+    <GrpcDotnetVersion>2.44.0</GrpcDotnetVersion>
 
     <!-- assembly version of grpc-dotnet -->
     <GrpcDotnetAssemblyVersion>2.0.0.0</GrpcDotnetAssemblyVersion>