Remove ota_close(int) and ota_fclose(FILE*).

We should always use unique_fd or unique_file to hold the FD or FILE*
pointer when opening via ota_(f)open functions.

This CL avoids accidentally closing raw FDs or FILE* pointers that are
managed by unique_fd/unique_file.

Test: recovery_component_test passes.
Change-Id: If58eb8b5c5da507563f85efd5d56276472a1c957