Windows package: remove spurious antislash

Introduced in 2ae88722

(cherry picked from commit 1abd50c2)
9 jobs for 4.6 in 232 minutes and 47 seconds (queued for 48 seconds)
Status Job ID Name Coverage
  Build
passed #15964
build_binaries

00:12:10

passed #15965
build_doc

00:01:58

 
  Test And Pkg
passed #15968
macOS
pkg_macOS

00:12:50

passed #15966
pkg_source

00:01:49

passed #15967
pkg_windows

00:24:12

passed #15972
test_dynare++

00:11:53

passed #15969
test_matlab

00:53:34

passed #15971
test_octave

03:38:48

passed #15970
test_old_matlab

01:34:13