tests: remove obsolete non-strict uid tests

tests: remove obsolete non-strict uid tests

Recently added strict tests for uid/gid related syscalls
made old uid tests obsolete.

* tests/uid.awk: Remove.
* tests/uid.c: Remove.
* tests/uid.test: Remove.
* tests/uid16.c: Remove.
* tests/uid16.test: Remove.
* tests/uid32.c: Remove.
* tests/uid32.test: Remove.
* tests/.gitignore: Remove uid, uid16, and uid32.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Remove uid.test, uid16.test, and uid32.test.
(EXTRA_DIST): Remove uid.awk.