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.

src/Makefile.am

@@ -321,7 +321,6 @@ libmodsecurity_la_CPPFLAGS = \
 	$(GEOIP_CFLAGS) \
 	$(GLOBAL_CPPFLAGS) \
 	$(MODSEC_NO_LOGS) \
-	$(MODSEC_MUTEX_ON_PM) \
 	$(YAJL_CFLAGS) \
 	$(LMDB_CFLAGS) \
 	$(PCRE_CFLAGS) \

src/operators/pm.cc

@@ -85,14 +85,7 @@ bool Pm::evaluate(Transaction *transaction, RuleWithActions *rule,
     pt.parser = m_p;
     pt.ptr = NULL;
     const char *match = NULL;
-#ifdef MODSEC_MUTEX_ON_PM
-    {
-    const std::lock_guard lock(m_mutex);
-#endif
     rc = acmp_process_quick(&pt, &match, input.c_str(), input.length());
-#ifdef MODSEC_MUTEX_ON_PM
-    }
-#endif
 
     if (rc >= 0 && transaction) {
         std::string match_(match?match:"");

src/operators/pm.h

@@ -53,12 +53,6 @@ class Pm : public Operator {
 
  protected:
     ACMP *m_p;
-
-#ifdef MODSEC_MUTEX_ON_PM
-
- private:
-    std::mutex m_mutex;
-#endif
 };