internal/lsp: fix infinite recursion in CancelRequest

Quick fix to (*server).CancelRequest, but we haven't implemented actual
support for it. Filed golang/go#35679 to track this.

Change-Id: Ic0de01d49b779c4f0656587584fbd2bf8791d0ce
Reviewed-on: https://go-review.googlesource.com/c/tools/+/207718
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/internal/lsp/server.go b/internal/lsp/server.go
index 843db24..c779ada 100644
--- a/internal/lsp/server.go
+++ b/internal/lsp/server.go
@@ -108,7 +108,7 @@
 }
 
 func (s *Server) CancelRequest(ctx context.Context, params *protocol.CancelParams) error {
-	return s.CancelRequest(ctx, params)
+	return nil
 }
 
 // Workspace