Remove Hlt directory to avoid compilation errors.

Compiling Moore as it is results in a few errors:

FAILED: Hlt/HltMonitoring/CMakeFiles/HltMonitoringLib.dir/src/ZmqMonitorSvc.cpp.o
In file included from ../Hlt/HltMonitoring/src/ZmqMonitorSvc.cpp:18:
../Hlt/HltMonitoring/src/ZmqMonitorSvc.h:24:10: fatal error: Hlt2Monitoring/Common.h: No such file or directory
   24 | #include <Hlt2Monitoring/Common.h>
(...)
FAILED: Hlt/HltMonitoring/CMakeFiles/HltMonitoringLib.dir/src/HltInfoSvc.cpp.o
In file included from ../Hlt/HltMonitoring/src/HltInfoSvc.cpp:24:
/afs/cern.ch/work/l/lmeyerga/stack_default_070421/LHCb/InstallArea/x86_64-centos7-gcc9-opt/include/zmq/zmq.hpp:71:10: fatal error: zmq.h: No such file or directory
(...)
FAILED: Hlt/HltMonitoring/CMakeFiles/HltMonitoringLib.dir/src/HltMonitorSvc.cpp.o
In file included from ../Hlt/HltMonitoring/src/HltMonitorSvc.cpp:23:
/afs/cern.ch/work/l/lmeyerga/stack_default_070421/LHCb/InstallArea/x86_64-centos7-gcc9-opt/include/zmq/zmq.hpp:71:10: fatal error: zmq.h: No such file or directory
(...)
FAILED: Hlt/HltMonitoring/CMakeFiles/HltMonitoringLib.dir/src/ZmqHistogramSvc.cpp.o
In file included from ../Hlt/HltMonitoring/src/ZmqHistogramSvc.cpp:60:
/afs/cern.ch/work/l/lmeyerga/stack_default_070421/LHCb/InstallArea/x86_64-centos7-gcc9-opt/include/zmq/zmq.hpp:71:10: fatal error: zmq.h: No such file or directory

This seems to be caused by Online!388 (merged) and Online!389 (merged).

FYI: @sstahl