Fix notifications hiding on Linux.

Regression was introduced in 3372dfcd3e.

Only when platform-specific code can give us the global time of the
last user input event we rely on idle time for notifications hiding.

Fixes #5791.

Telegram/SourceFiles/platform/linux/specific_linux.cpp

@@ -193,10 +193,6 @@ void psDeleteDir(const QString &dir) {
 	_removeDirectory(dir);
 }
 
-bool psIdleSupported() {
-	return false;
-}
-
 void psActivateProcess(uint64 pid) {
 //	objc_activateProgram();
 }
@@ -435,10 +431,6 @@ bool OpenSystemSettings(SystemSettingsType type) {
 	return true;
 }
 
-crl::time LastUserInputTime() {
-	return 0LL;
-}
-
 namespace ThirdParty {
 
 void start() {