[libc][Obvious] Fix llvm_libc_ext.td.

GitOrigin-RevId: aeee014428ac5d4e639815541dbff5e298245064
diff --git a/spec/llvm_libc_ext.td b/spec/llvm_libc_ext.td
index cffeb2e..d4a133a 100644
--- a/spec/llvm_libc_ext.td
+++ b/spec/llvm_libc_ext.td
@@ -10,15 +10,6 @@
               RetValSpec<VoidType>,
               [ArgSpec<VoidPtr>, ArgSpec<SizeTType>]
           >,
-      ]
-  >;
-
-  HeaderSpec String = HeaderSpec<
-      "string.h",
-      [], // Macros
-      [], // Types
-      [], // Enumerations
-      [
           FunctionSpec<
               "bcmp",
               RetValSpec<IntType>,