runtests: drop orphaned, no-op -k option

And the corresponding internal variable.

This option became the always-enabled default earlier, via #4035.

Reported-by: Zartaj Majeed
Ref: #22098
Follow-up to 6617db6a7e #4035

Closes #22100

docs/runtests.md

@@ -164,11 +164,6 @@ CPU cores is a good figure to start with, or 1.3 times if Valgrind is in use,
 or 5 times for torture tests. Enabling parallel tests is not recommended in
 conjunction with the -g option.
 
-## `-k`
-
-Keep output and log files in log/ after a test run, even if no error was
-detected. Useful for debugging.
-
 ## `-L \<file\>`
 
 Load and execute the specified file which should contain perl code. This

tests/runtests.pl

@@ -182,7 +182,6 @@ my %runnersrunning;    # tests currently running by runner ID
 #
 my $short;
 my $no_debuginfod;
-my $keepoutfiles; # keep stdout and stderr files after tests
 my $postmortem;   # display detailed info about failed tests
 my $run_disabled; # run the specific tests even if listed in DISABLED
 my $scrambleorder;
@@ -2540,10 +2539,6 @@ while(@ARGV) {
             $jobs = $1;
         }
     }
-    elsif($ARGV[0] eq "-k") {
-        # keep stdout and stderr files after tests
-        $keepoutfiles = 1;
-    }
     elsif($ARGV[0] eq "-r") {
         # run time statistics needs Time::HiRes
         if($Time::HiRes::VERSION) {
@@ -2596,7 +2591,6 @@ Usage: runtests.pl [options] [test selection(s)]
   -gw      run the test case with gdb as a windowed application
   -h       this help text
   -j[N]    spawn this number of processes to run tests (default 0)
-  -k       keep stdout and stderr files present after tests
   -L path  require an additional perl library file to replace certain functions
   -l       list all test case names/descriptions
   -m=[seconds] set timeout for curl commands in tests