Makefile: Generate .NOTPARALLEL without .PHONY (#14312)

In commit v3.0.0-rc1~222^2 (Makefile: Allow "gmake target1 target2 -j",
2013-12-18) we added generation of a .NOTPARALLEL rule and told the
generator it is "symbolic" because the file will never be created.
This causes ".PHONY" to be used.  However, "clearmake" does not support
parsing of .PHONY specifically for .NOTPARALLEL, so simply drop it.
This should not affect the role of the .NOTPARALLEL rule for GNU make.

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -1826,7 +1826,7 @@ void cmLocalUnixMakefileGenerator3
     std::vector<std::string> no_depends;
     this->WriteMakeRule(ruleFileStream,
       "Allow only one \"make -f Makefile2\" at a time, but pass parallelism.",
-      ".NOTPARALLEL", no_depends, no_commands, true);
+      ".NOTPARALLEL", no_depends, no_commands, false);
     }
   }