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/IntrusionSensorMain.cpp b/src/intrusion/IntrusionSensorMain.cpp
index c94727a..bc096c4 100644
--- a/src/intrusion/IntrusionSensorMain.cpp
+++ b/src/intrusion/IntrusionSensorMain.cpp
@@ -389,15 +389,16 @@
     getNicNameInfo(conn);
 
     // get eth info from sysfs
-    std::vector<fs::path> files;
-    if (!findFiles(fs::path("/sys/class/net/"), R"(eth\d+/ifindex)", files))
+    std::vector<std::filesystem::path> files;
+    if (!findFiles(std::filesystem::path("/sys/class/net/"),
+                   R"(eth\d+/ifindex)", files))
     {
         std::cerr << "No eth in system\n";
         return false;
     }
 
     // iterate through all found eth files, and save ifindex
-    for (const fs::path& fileName : files)
+    for (const std::filesystem::path& fileName : files)
     {
         if (debugLanLeash)
         {