Remove reference to `diy-fp.cc`

That file was removed in a previous commit.

Fixes #112

CMakeLists.txt

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bc4bdad..a51add2 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -18,7 +18,6 @@
             double-conversion/bignum.cc
             double-conversion/bignum-dtoa.cc
             double-conversion/cached-powers.cc
-            double-conversion/diy-fp.cc
             double-conversion/double-to-string.cc
             double-conversion/fast-dtoa.cc
             double-conversion/fixed-dtoa.cc