Remove index out of range assertions from Array getters

A lot of code seems to have been incompatible with the recently removed DEBUG_MEM flag, i.e. it relied on the Array getters returning a null object when the index was out of range and rather checked the returned object type (since they had to do that in any case) than the index.

Due to this, debug builds became much harder to test, especially using fuzzing. This commit thereby removes the assertions to restore the situation when DEBUG_MEM was present but disabeld by default and should thereby fix oss-fuzz/10121.