Revert "SAI proposal for icmp echo offload (#1943)" (#1969)

This reverts commit c1e840b.

Author: kcudnik

doc/SAI-Proposal-ICMP-ECHO_Extensions.md

@@ -45,7 +45,6 @@
 #include "saiexperimentaldashdirectionlookup.h"
 #include "saiexperimentaldashacl.h"
 #include "saiexperimentalbmtor.h"
-#include "saiexperimentalicmpecho.h"
 
 /**
  * @brief Extensions to SAI APIs
@@ -78,8 +77,6 @@ typedef enum _sai_api_extensions_t
 
     SAI_API_DASH_VIP,
 
-    SAI_API_ICMP_ECHO,
-
     /* Add new experimental APIs above this line */
 
     SAI_API_EXTENSIONS_RANGE_END