Revert "Fixed crash issue in RawSerial::printf for uARM"

This reverts commit d05b7f51d8.

I am reverting this commit because:

- it uses alloca(), which is a dangerous function
- it uses vsprintf instead of vsnprintf, which can lead to a stack overflow.

Until we find a better solution, this might do more bad than good, so I am reverting it.

libraries/mbed/common/RawSerial.cpp

@@ -47,13 +47,6 @@ int RawSerial::puts(const char *str) {
 int RawSerial::printf(const char *format, ...) {
     std::va_list arg;
     va_start(arg, format);
-#if defined(__MICROLIB) && defined(__ARMCC_VERSION) // with microlib and ARM compiler
-    char *temp;
-    temp = (char*)alloca(STRING_STACK_LIMIT);
-    vsprintf(temp, format, arg);
-    puts(temp);
-    int len = strlen(temp);
-#else
     int len = vsnprintf(NULL, 0, format, arg);
     if (len < STRING_STACK_LIMIT) {
         char temp[STRING_STACK_LIMIT];
@@ -65,7 +58,6 @@ int RawSerial::printf(const char *format, ...) {
         puts(temp);
         delete[] temp;
     }
-#endif
     va_end(arg);
     return len;
 }