rm: fix sign comparison warnings

There are multiple places in loops, where a signed and an unsigned data type are compared. Git uses a mix of signed and unsigned types to store lengths of arrays. This sometimes leads to using a signed index for an array whose length is stored in an unsigned variable or vice versa. get_ours_cache_pos is a special case where i, though derived from a signed variable is never negative. Move this part to the caller side and make i an unsigned argument of the function. Rename i to pos to make it descriptive, now that it is a function argument. Replace signed data types with unsigned data types and vice versa wherever necessary. Where both signed and unsigned data types have been used, define a new variable in the scope of the for loop for use as the iterator. Remove #define DISABLE_SIGN_COMPARE_WARNINGS. Signed-off-by: Arnav Bhate <bhatearnav@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>