Removed unnecessary lock to call acmp_process_quick in Pm::evaluate

- This was introduced in commit 119a6fc & 7d786b3 because of a potential
  issue reported in #1573.
- The ACMP tree structure is initialized when the operator is
  initialized.
- During transaction execution the ACMP tree structure is only 'read'
  while traversing the tree (in acmp_process_quick) so this is safe for
  use in a multi-threaded environment.

configure.ac

@@ -316,23 +316,6 @@ AC_ARG_ENABLE(parser-generation,
     [buildParser=false]
     )
 
-# Mutex
-AC_ARG_ENABLE(mutex-on-pm,
-    [AS_HELP_STRING([--enable-mutex-on-pm],[Treats pm operations as a critical section])],
-
-    [case "${enableval}" in
-        yes) mutexPm=true ;;
-        no)  mutexPm=false ;;
-        *) AC_MSG_ERROR(bad value ${enableval} for --enable-mutex-on-pm) ;;
-    esac],
-
-    [mutexPm=false]
-    )
-if test "$mutexPm" == "true"; then
-    MODSEC_MUTEX_ON_PM="-DMUTEX_ON_PM=1"
-    AC_SUBST(MODSEC_MUTEX_ON_PM)
-fi
-
 
 if test $buildParser = true; then
     AC_PROG_YACC