[diag] remove diag sleep command (#2378)

So then platforms could define their own sleep behavior.

src/diag/diag_process.cpp

@@ -52,7 +52,6 @@ const struct Command Diag::sCommands[] =
     { "power", &ProcessPower },
     { "send", &ProcessSend },
     { "repeat", &ProcessRepeat },
-    { "sleep", &ProcessSleep },
     { "stats", &ProcessStats },
 };
 
@@ -304,21 +303,6 @@ exit:
     AppendErrorResult(error, aOutput, aOutputMaxLen);
 }
 
-void Diag::ProcessSleep(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen)
-{
-    otError error = OT_ERROR_NONE;
-
-    VerifyOrExit(otPlatDiagModeGet(), error = OT_ERROR_INVALID_STATE);
-
-    otPlatRadioSleep(sContext);
-    snprintf(aOutput, aOutputMaxLen, "sleeping now...\r\n");
-
-exit:
-    OT_UNUSED_VARIABLE(argc);
-    OT_UNUSED_VARIABLE(argv);
-    AppendErrorResult(error, aOutput, aOutputMaxLen);
-}
-
 void Diag::ProcessStats(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen)
 {
     otError error = OT_ERROR_NONE;

src/diag/diag_process.hpp

@@ -76,7 +76,6 @@ public:
 
 private:
     static void AppendErrorResult(otError error, char *aOutput, size_t aOutputMaxLen);
-    static void ProcessSleep(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen);
     static void ProcessStart(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen);
     static void ProcessStop(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen);
     static void ProcessSend(int argc, char *argv[], char *aOutput, size_t aOutputMaxLen);

tests/unit/test_diag.cpp

@@ -139,10 +139,6 @@ void TestDiag()
             "diag repeat 100 100\n",
             "sending packets of length 0x64 at the delay of 0x64 ms\r\nstatus 0x00\r\n"
         },
-        {
-            "diag sleep\n",
-            "sleeping now...\r\n",
-        },
         {
             "diag stop\n",
             "received packets: 0\r\nsent packets: 0\r\nfirst received packet: rssi=0, lqi=0\r\n\nstop diagnostics mode\r\nstatus 0x00\r\n",