edify: Switch to C++.

Change-Id: I71aede6e29af1dc4bb858a62016c8035db5d3452
diff --git a/edify/expr.h b/edify/expr.h
index a9ed2f9..36f8e96 100644
--- a/edify/expr.h
+++ b/edify/expr.h
@@ -21,10 +21,6 @@
 
 #include "yydefs.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #define MAX_STRING_LEN 1024
 
 typedef struct Expr Expr;
@@ -59,7 +55,7 @@
 
 struct Expr {
     Function fn;
-    char* name;
+    const char* name;
     int argc;
     Expr** argv;
     int start, end;
@@ -166,8 +162,4 @@
 
 int parse_string(const char* str, Expr** root, int* error_count);
 
-#ifdef __cplusplus
-}  // extern "C"
-#endif
-
 #endif  // _EXPRESSION_H