CMake: remove broken logic to install empty database directory

The CMake code to install the empty database directory doesn't appear to
do anything.  Further, it is causing build issues for some users.

I tested some with trying to install the database directory directly,
like this:

```cmake
if(IS_ABSOLUTE ${DATABASE_DIRECTORY})
    INSTALL(DIRECTORY DESTINATION $ENV{DESTDIR}${DATABASE_DIRECTORY} COMPONENT programs)
else()
    INSTALL(DIRECTORY DESTINATION $ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/${DATABASE_DIRECTORY} COMPONENT programs)
endif()
```

However, this causes build failures for Windows and macOS installers.

Windows:
```
CMake Error at C:/Users/build/Documents/jenkins/workspace/test-pipelines_build-1.3/clamav-devel/build64/freshclam/cmake_install.cmake:66 (message):

  ABSOLUTE path INSTALL DESTINATION forbidden (by caller):

  C:/Users/build/Documents/jenkins/workspace/test-pipelines_build-1.3/clamav-devel/build64/install/database/

Call Stack (most recent call first):

  C:/Users/build/Documents/jenkins/workspace/test-pipelines_build-1.3/clamav-devel/build64/cmake_install.cmake:133 (include)
```

macOS:
```
CMake Error at /Users/****/jenkins/workspace/test-pipelines_build-1.3/clamav-devel/build-pkg/freshclam/cmake_install.cmake:111 (file):
  file INSTALL cannot make directory "/usr/local/clamav/share/clamav": No
  such file or directory.

Call Stack (most recent call first):
  /Users/****/jenkins/workspace/test-pipelines_build-1.3/clamav-devel/build-pkg/cmake_install.cmake:122 (include)

CPack Error: Error when generating package: ClamAV
```

I think my best option is just to remove this line of code since it's causing
problems for some and isn't working for anyone. Even if it would be
nice to have the database directory created at install time automatically.

Fixes: #1142

freshclam/CMakeLists.txt

@@ -46,9 +46,6 @@ else()
     install(TARGETS freshclam-bin DESTINATION ${CMAKE_INSTALL_BINDIR} COMPONENT programs)
 endif()
 
-# Install an empty database directory
-INSTALL(CODE "FILE(MAKE_DIRECTORY \${ENV}\${CMAKE_INSTALL_PREFIX}/\${DATABASE_DIRECTORY})" COMPONENT programs)
-
 # Now we rename freshclam-bin executable to freshclam using target properties
 set_target_properties( freshclam-bin
         PROPERTIES OUTPUT_NAME freshclam )