Reliably kill test processes

It seems command -v also includes built-ins so checking for kill
is useless because it finds the built-in and those machines or
environments that have no /bin/kill fail at the check stage.
Oh and then TCL exec doesn't spawn a shell.

After reading way too many TCL websites, I believe this should
fix the problem. TCL quoting is... different to say the least but
it works reliably here. The script now even picked up a typo elsewhere
which was nice.

This change should stop the intermittent FTBFS bugs from the Debian
pbuilders, I hope! You'd think kill $var wouldn't be this difficult.

testsuite/pkill.test/pkill.exp

@@ -16,12 +16,6 @@ set test "pkill with no arguments"
 spawn $pkill
 expect_pass "$test" "^\(lt-\)\?pkill: no matching criteria specified\\s*"
 
-# Tests that don't need the test process go above here
-if { [ catch { exec sh -c "command -v kill" } kill_path] } {
-  untested { kill path not found }
-  return
-}
-
 make_testproc
 set testproc_len [ string length $testproc_comm ]
 set testproc_trim [ string range $testproc_comm 0 [ expr { $testproc_len - 2 } ] ]
@@ -132,6 +126,4 @@ untested "$test"
 
 
 # Cleanup
-eval exec "$kill_path $testproc1_pid"
-eval exec "$kill_path $testproc2_pid"
-exec rm $testproc_path
+kill_testproc