Deprecate std::filesystem namespace include

Clang-tidy is complaining about our using fs = ... directives.  These
were originally added to handle boost::filesystem vs
std::experimental::filesystem vs std::filesystem between the various
compilers.  Now that we're all on std::filesystem, this redefinition can
be removed.

```
ChassisIntrusionSensor.hpp:11:11: error: namespace alias decl 'fs' is unused [misc-unused-alias-decls,-warnings-as-errors]
   11 | namespace fs = std::filesystem;
```

Tested: code compiles

Change-Id: If4b968ff9cceb4038f526321d3c7c11563ffbce9
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/src/intrusion/ChassisIntrusionSensor.cpp b/src/intrusion/ChassisIntrusionSensor.cpp
index 2c1e391..9740007 100644
--- a/src/intrusion/ChassisIntrusionSensor.cpp
+++ b/src/intrusion/ChassisIntrusionSensor.cpp
@@ -441,9 +441,10 @@
     ChassisIntrusionSensor(autoRearm, objServer),
     mHwmonName(std::move(hwmonName)), mPollTimer(io)
 {
-    std::vector<fs::path> paths;
+    std::vector<std::filesystem::path> paths;
 
-    if (!findFiles(fs::path("/sys/class/hwmon"), mHwmonName, paths))
+    if (!findFiles(std::filesystem::path("/sys/class/hwmon"), mHwmonName,
+                   paths))
     {
         throw std::invalid_argument("Failed to find hwmon path in sysfs\n");
     }