[BUG] lib_outstream_s putc and puts are redundant

### Description / Steps to reproduce the issue

lib_outstream_s has two seemingly-redundant methods, one for single-char operation and another for multi-chars operation, for no obvious reasons. (well, at least not obvious to me.)
if it's necessary for some reasons, it should have been commented in the code.
otherwise, one of them, maybe the single-char version which is likely slower, should be removed to save code size.

ditto for
* lib_instream_s getc and gets
* syslog_putc and syslog_write
* syslog sc_putc/sc_force and sc_write/sc_write_force
* up_putc and up_nputs

### On which OS does this issue occur?

[OS: Mac]

### What is the version of your OS?

macOS 14.7

### NuttX Version

master

### Issue Architecture

[Arch: all]

### Issue Area

[Area: Api]

### Verification

- [X] I have verified before submitting the report.