configTime(tzsec,dstsec,): fix UTC/local management (#6993)

* configTime(tzsec,dstsec,): fix UTC/local management
This PR also remove dead code since probably newlib updates
The NTP-TZ-DST example is also updated
* restore sntp_set_timezone_in_seconds()
fixes #6678
* +configTzTime()

Author: d-a-v

cores/esp8266/Arduino.h

@@ -281,6 +281,13 @@ void configTime(int timezone, int daylightOffset_sec, const char* server1,
 void configTime(const char* tz, const char* server1,
     const char* server2 = nullptr, const char* server3 = nullptr);
 
+// esp32 api compatibility
+inline void configTzTime(const char* tz, const char* server1,
+    const char* server2 = nullptr, const char* server3 = nullptr)
+{
+    configTime(tz, server1, server2, server3);
+}
+
 #endif // __cplusplus
 
 #include "pins_arduino.h"

cores/esp8266/coredecls.h

@@ -13,12 +13,14 @@ extern "C" {
 #include <cont.h> // g_pcont declaration
 
 extern bool timeshift64_is_set;
+extern uint32_t sntp_real_timestamp;
 
 bool can_yield();
 void esp_yield();
 void esp_schedule();
 void tune_timeshift64 (uint64_t now_us);
 void disable_extra4k_at_link_time (void) __attribute__((noinline));
+bool sntp_set_timezone_in_seconds(int32_t timezone);
 
 uint32_t sqrt32 (uint32_t n);
 uint32_t crc32 (const void* data, size_t length, uint32_t crc = 0xffffffff);