Delete unused files

This directory contains several simple utilities that either are not used or can be replaced with simpler tools:
- args.c: not used
- echoout.c: used once in Macaulay2/d to reverse a list. Possible alternative:
- `alias tac='perl -e "print reverse(<>)"'` (in case `tac` doesn't already exist)
- `(for d in ${MY_LIST}; do echo $$d; done) | tac`
- gc_demo.c: not used, though perhaps useful to keep it somewhere else for pedagogy.
- gc_test.c: used as a test, can be moved to Macaulay2/tests
- linkexec*: seems to be an overly complicated solution to making the programs relocatable
- setup.c: windows legacy
- timestamp.c: compiled, but not used as far as I can tell

Start by inspecting the directory and searching build files and source references for args.c, echoout.c, gc_demo.c, gc_test.c, linkexec*, setup.c, and timestamp.c. Check the use of echoout.c in Macaulay2/d and the proposed destination Macaulay2/tests for gc_test.c. Done means each listed utility has a documented disposition: removed, moved, or replaced as described.

Written by the indexing model from the issue text.