runtests: drop logic calling the `handle` tool (Windows)

runtests: drop logic calling the `handle` tool (Windows)

In the cases observed throughout the last year, `handle64` run once per
test run, but with no action (match or task kill). It did not help with
flakiness and seems redundant.

runtests launched it (if present) in Cygwin/MSYS jobs too, where it
probably shouldn't have, because we have seen no flakiness there. In CI
the tool was present and launched in MSYS2 jobs, but not in Cygwin.

After this patch the "clearlocks" warning remain in the log. They are
consistently appearing once in every MSVC CI log, early in the tests:
```
  test 3207 SKIPPED: curl lacks OpenSSL support
[...START-OF-TESTS...]
  test 0003...[HTTP POST with auth and contents but with content-length set to 0]
  --pd---e--- OK (3   out of 1596, remaining: 17:50, took 1.423s, duration: 00:02)
  test 0007...[HTTP with cookie parser and header recording]
  --pd--oe--- OK (7   out of 1596, remaining: 07:51, took 1.485s, duration: 00:02)
  test 0006...[HTTP with simple cookie send]
  --pd---e--- OK (6   out of 1596, remaining: 09:11, took 1.488s, duration: 00:02)
  test 0005...[HTTP over proxy]
  --pd---e--- OK (5   out of 1596, remaining: 11:03, took 1.491s, duration: 00:02)
CUSTOMBUILD : error : 169: cleardir(log/8/lock) failed [D:\a\curl\curl\bld\tests\test-ci.vcxproj]
  test 0001...[HTTP GET]
  --pd---e--- OK (1   out of 1596, remaining: 55:34, took 1.466s, duration: 00:02)
  test 0004...[Replaced internal and added custom HTTP headers]
```
Ref: https://github.com/curl/curl/actions/runs/13546192228/job/37858323380?pr=16484#step:14:167

Ref: e53523fef07894991c69d907a7c7794c7ada4ff4 #14859
Ref: 311c31ec8e721b11ba77adf7a3865cf0cd30aa42 #6179
Follow-up to 3a8920e5edaead8304a818594f54485a5564f976 #16600
Closes #16484