setup_venv: Add pkg-config to VENV_DEPENDENCIES.
setup_venv: Add pkg-config to VENV_DEPENDENCIES.

This is needed on at least Debian 10, otherwise xmlsec fails to
install: `Could not find xmlsec1 config. Are libxmlsec1-dev and
pkg-config installed?`

Also remove libxmlsec1-openssl, which libxmlsec1-dev already depends.

(No changes are needed on RHEL, where libxml2-devel and xmlsec1-devel
already declare a requirement on /usr/bin/pkg-config.)

Signed-off-by: Anders Kaseorg <dfdb7392591db597bc41cf266a9c3bc12a2706e5@zulipchat.com>

hackerkid/zulip,shubhamdhama/zulip,synicalsyntax/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,andersk/zulip,shubhamdhama/zulip,zulip/zulip,andersk/zulip,shubhamdhama/zulip,andersk/zulip,kou/zulip,andersk/zulip,showell/zulip,synicalsyntax/zulip,rht/zulip,kou/zulip,showell/zulip,showell/zulip,zulip/zulip,zulip/zulip,eeshangarg/zulip,shubhamdhama/zulip,rht/zulip,rht/zulip,andersk/zulip,zulip/zulip,shubhamdhama/zulip,eeshangarg/zulip,punchagan/zulip,zulip/zulip,synicalsyntax/zulip,showell/zulip,synicalsyntax/zulip,brainwane/zulip,rht/zulip,brainwane/zulip,hackerkid/zulip,rht/zulip,andersk/zulip,hackerkid/zulip,brainwane/zulip,timabbott/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,punchagan/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,timabbott/zulip,showell/zulip,rht/zulip,punchagan/zulip,brainwane/zulip,timabbott/zulip,hackerkid/zulip,showell/zulip,punchagan/zulip,punchagan/zulip,brainwane/zulip,hackerkid/zulip,brainwane/zulip,eeshangarg/zulip,timabbott/zulip,timabbott/zulip,punchagan/zulip,kou/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,zulip/zulip,showell/zulip,brainwane/zulip,synicalsyntax/zulip,timabbott/zulip,kou/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip