appveyor: drop VS2008 CI job, move OpenSSL 1.0.2 to VS2010

appveyor: drop VS2008 CI job, move OpenSSL 1.0.2 to VS2010

It became flaky today, possible due to an upstream issue. Drop this CI job
also because VS2008 is going to be deprecated soon.

Example:
```
1>------ Build started: Project: curlu, Configuration: Debug Win32 ------
1>Compiling...
1>Project : error PRJ0003 : Error spawning 'cl.exe'.
1>Build log was saved at "file://c:\projects\curl\_bld\lib\curlu.dir\Debug\BuildLog.htm"
1>curlu - 1 error(s), 0 warning(s)
[...]
8>Linking...
8>LINK : fatal error LNK1104: cannot open file '..\..\lib\Debug\curlu-d.lib'
8>Build log was saved at "file://c:\projects\curl\_bld\tests\unit\units.dir\Debug\BuildLog.htm"
8>Test units - 1 error(s), 0 warning(s)
[...]
========== Build: 7 succeeded, 2 failed, 5 up-to-date, 0 skipped ==========
[...]
Command exited with code 1
```

Other times with no visible error all:
```
========== Build: 9 succeeded, 0 failed, 5 up-to-date, 0 skipped ==========
[...]
Command exited with code 1
```
Ref: https://ci.appveyor.com/project/curlorg/curl/builds/52330703/job/ooqxq0b8ftbsv640#L413

Follow-up to 8c9a9b87c20fd9184e0a6c7b5e2c42d727f0db62 #17725
Follow-up to 63e513b106113db0b1b68bab347b80cb4cef4e65 #17380

Closes #17798