remove the unnecessary header file inclusion

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

example.c

@@ -8,7 +8,6 @@
 
 #include <stdio.h>
 #include <string.h>
-#include <ctype.h>
 
 #include "minmea.h"
 

minmea.c

@@ -12,7 +12,6 @@
 #include <string.h>
 #include <ctype.h>
 #include <stdarg.h>
-#include <time.h>
 
 #define boolstr(s) ((s) ? "true" : "false")
 

minmea.h

@@ -13,10 +13,8 @@
 extern "C" {
 #endif
 
-#include <stdio.h>
 #include <stdint.h>
 #include <stdbool.h>
-#include <errno.h>
 #include <time.h>
 #include <math.h>
 #ifdef MINMEA_INCLUDE_COMPAT

tests.c

@@ -11,7 +11,6 @@
 
 #include <stdlib.h>
 #include <string.h>
-#include <math.h>
 #include <check.h>
 
 #include "minmea.h"