py/malloc: Remove unneeded code checking m_malloc return value.

m_malloc already checks for a failed allocation so there's no need to check
for it in m_malloc0.

py/malloc.c

@@ -117,9 +117,6 @@ void *m_malloc_with_finaliser(size_t num_bytes) {
 
 void *m_malloc0(size_t num_bytes) {
     void *ptr = m_malloc(num_bytes);
-    if (ptr == NULL && num_bytes != 0) {
-        m_malloc_fail(num_bytes);
-    }
     // If this config is set then the GC clears all memory, so we don't need to.
     #if !MICROPY_GC_CONSERVATIVE_CLEAR
     memset(ptr, 0, num_bytes);