Remove checks for LXC containers used under Travis CI only

As we don't use Travis CI any longer, we don't need these checks
neither.

tests/file/filetest.cpp

@@ -141,11 +141,6 @@ void FileTestCase::TempFile()
 // Check that GetSize() works correctly for special files.
 TEST_CASE("wxFile::Special", "[file][linux][special-file]")
 {
-    // LXC containers don't (always) populate /proc and /sys, so skip these
-    // tests there.
-    if ( IsRunningInLXC() )
-        return;
-
     // We can't test /proc/kcore here, unlike in the similar
     // wxFileName::GetSize() test, as wxFile must be able to open it (at least
     // for reading) and usually we don't have the permissions to do it.

tests/filename/filenametest.cpp

@@ -949,9 +949,6 @@ TEST_CASE("wxFileName::Shortcuts", "[filename]")
 // Check that GetSize() works correctly for special files.
 TEST_CASE("wxFileName::GetSizeSpecial", "[filename][linux][special-file]")
 {
-    if ( IsRunningInLXC() )
-        return;
-
     wxULongLong size = wxFileName::GetSize("/proc/kcore");
     INFO( "size of /proc/kcore=" << size );
     CHECK( size > 0 );

tests/test.cpp

@@ -424,20 +424,6 @@ extern bool IsRunningUnderXVFB()
     return s_isRunningUnderXVFB == 1;
 }
 
-#ifdef __LINUX__
-
-extern bool IsRunningInLXC()
-{
-    // We're supposed to be able to detect running in LXC by checking for
-    // /dev/lxd existency, but this doesn't work under Travis for some reason,
-    // so just rely on having the environment variable defined for the
-    // corresponding builds in our .travis.yml.
-    wxString value;
-    return wxGetEnv("wxLXC", &value) && value == "1";
-}
-
-#endif // __LINUX__
-
 #if wxUSE_GUI
 
 bool EnableUITests()

tests/testprec.h

@@ -147,10 +147,6 @@ extern bool IsAutomaticTest();
 
 extern bool IsRunningUnderXVFB();
 
-#ifdef __LINUX__
-extern bool IsRunningInLXC();
-#endif // __LINUX__
-
 // Helper class setting the locale to the given one for its lifetime.
 class LocaleSetter
 {

tests/textfile/textfiletest.cpp

@@ -341,11 +341,6 @@ void TextFileTestCase::ReadBig()
 // correspond to the real amount of data in them, works.
 TEST_CASE("wxTextFile::Special", "[textfile][linux][special-file]")
 {
-    // LXC containers don't (always) populate /proc and /sys, so skip these
-    // tests there.
-    if ( IsRunningInLXC() )
-        return;
-
     SECTION("/proc")
     {
         wxTextFile f;