Remove non-existent files from BUILD.gn (#2955)

Fixes #2954
diff --git a/BUILD.gn b/BUILD.gn
index a8bd134..2418e0b 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -734,10 +734,6 @@
     "source/reduce/remove_function_reduction_opportunity_finder.h",
     "source/reduce/remove_instruction_reduction_opportunity.cpp",
     "source/reduce/remove_instruction_reduction_opportunity.h",
-    "source/reduce/remove_opname_instruction_reduction_opportunity_finder.cpp",
-    "source/reduce/remove_opname_instruction_reduction_opportunity_finder.h",
-    "source/reduce/remove_relaxed_precision_decoration_opportunity_finder.cpp",
-    "source/reduce/remove_relaxed_precision_decoration_opportunity_finder.h",
     "source/reduce/remove_selection_reduction_opportunity.cpp",
     "source/reduce/remove_selection_reduction_opportunity.h",
     "source/reduce/remove_selection_reduction_opportunity_finder.cpp",