[C++][CI] Remove support for VisualStudio 2015

[asfimport]

MSVC 19.0 is buggy enough that I for one have spent multiple days
reworking code that is fine for all other compilers we test against.
Most recently in the context of #10793
(ARROW-13482) I found that for some types T,
std::is_convertible<T, T>::value will be false. This necessitated the
following
(very hacky) workaround:

c44be29

See mailing list discussion here: https://lists.apache.org/thread.html/rff3d8e837aee2964b49733b39a34cffef7c5438dbf2e5c929e878fdf%40%3Cdev.arrow.apache.org%3E

Reporter: Ben Kietzman / @bkietz
Assignee: Ben Kietzman / @bkietz

PRs and other links:

• GitHub Pull Request #11211

_{Note: This issue was originally created as ARROW-14070. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 11211
#11211