doc: remove incorrect mention of PR_GET_NAME

By removing the whole comment. These #include // For comments are near impossible
to maintain, pollute diffs, and generally don't add a lot of value.

src/util/threadnames.cpp

@@ -16,7 +16,7 @@
 #include <util/threadnames.h>
 
 #ifdef HAVE_SYS_PRCTL_H
-#include <sys/prctl.h> // For prctl, PR_SET_NAME, PR_GET_NAME
+#include <sys/prctl.h>
 #endif
 
 //! Set the thread's name at the process level. Does not affect the