Dropped SQL Server 2008 support

[morozov]

Q	A
Type	improvement
BC Break	yes

Fixes #3755.

Additionally, some changes in .appveyor.yml were needed in order to work around the build failure. The reason is:

1. Due to Not all package versions are returned when running running choco list --all-versions --exact chocolatey/choco#1843, choco search only returns PHP 7.4.0 as of today:

   PS C:\Users\Sergei Morozov> choco search php --exact --all-versions
   Chocolatey v0.10.15
   php 7.4.0 [Approved]
   1 packages found.
   
2. Combined with | select-string -pattern 7.3, it yields an empty list and fails the build.
3. Prior to this change, the builds would pass because all runtime dependencies are cached based on the content of .appveyor.yml.
4. We cannot switch to PHP 7.4 on AppVeyor because the corresponding sqlsrv and pdo_sqlsrv binaries are not yet available.

[SenseException]

Are we going to create a new PR for having sqlsrv and pdo_sqlsrv with PHP 7.4 when it is available? Or do you want to try to find another solution?

[morozov]

Are we going to create a new PR for having sqlsrv and pdo_sqlsrv with PHP 7.4 when it is available? Or do you want to try to find another solution?

Apparently, the 5.7.1preview builds are compiled for PHP 7.4 but I'd rather solve one problem at a time.

[beberlei]

@morozov this needs to get into 2.10 as well as appveyor is mass failing there as well