Remove unused macros

Remove unused macros

In the order of appearance:

* MAX_LISTEN - never used
  added by 23ad665c (qemud) and addec57 (lock daemon)

* NEXT_FREE_CLASS_ID - never used, added by 07d1b6b

* virLockError - never used, added by eb8268a4

* OPENVZ_MAX_ARG, CMDBUF_LEN, CMDOP_LEN
  unused since the removal of ADD_ARG_LIT in d8b31306

* QEMU_NB_PER_CPU_STAT_PARAM - unused since 897808e

* QEMU_CMD_PROMPT, QEMU_PASSWD_PROMPT - unused since 1dc10a7

* TEST_MODEL_WORDSIZE - unused since c25c18f7

* TEMPDIR - never used, added by 714bef5

* NSIG - workaround around old headers
  added by commit 60ed1d2
  unused since virExec was moved by commit 02e8691

* DO_TEST_PARSE - never used, added by 9afa006

* DIFF_MSEC, GETTIMEOFDAY - unused since eee6eb6