cmake/vcxproj: stop special-casing `remote-ext`

cmake/vcxproj: stop special-casing `remote-ext`

When the `vcxproj` target was introduced in `config.mak.uname` to allow
building Git with the Visual C toolchain, the `git remote-ext` command
was always executed in its dashed form. Therefore, it was impossible to
pass the test suite unless that command existed in its dashed form, and
we had to special-case this.

Later, when the `vcxproj` target got out of fashion because Visual
Studio gained native support for CMake builds, this special-casing was
copied without questioning it.

But as of 675df192c5f (transport-helper: do not run git-remote-ext etc.
in dashed form, 2020-08-26), the reason for this special-casing no
longer exists. So let's just drop it.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>