appveyor: Fix caching of OpenSSL installer.

Apparently, if the cache dependency is specified, the cache folder
is not checked at the end of a build and so the cache is never
updated unless we change appveyor.yml.  This makes the cache to not
actually work, because on each build we discover that the installer
is outdated, download the new one and it is not uploaded to the cache,
so it is still outdated on the next build.

Removing the dependency to get a normal cache behavior.  We're
manually comparing the hash of the cached binary with the most
latest one, so we will still catch any OpenSSL updates, but now
we will also upload the updated cache back.

Fixes: 9d82084 ("appveyor: Build with OpenSSL 3.0.")
Reported-at: https://help.appveyor.com/discussions/problems/36144-cache-reports-up-to-date-while-it-is-not
Acked-by: Alin-Gabriel Serdean <[email protected]>
Signed-off-by: Ilya Maximets <[email protected]>

appveyor.yml

@@ -15,7 +15,7 @@ init:
                               -Value "C:\Python312-x64\python.exe"
 
 cache:
-- C:\ovs-build-downloads -> appveyor.yml
+- C:\ovs-build-downloads
 
 install:
 - ps: |