build: remove the duplicate `make install-dep` in `make pkg-verify`

build: remove the duplicate `make install-dep` in `make pkg-verify`

In Makefile, when a target has multiple prerequisites, the order of
execution of prerequisites is not guaranteed. So we might encounter the
following `apt-get` lock issue when executing `make pkg-verify` due to
the duplicate execution of `make install-dep` command.

Reading package lists...
E: Could not get lock /var/lib/apt/lists/lock. It is held by process 21872 (apt-get)
E: Unable to lock directory /var/lib/apt/lists/
make[1]: *** [Makefile:404: install-dep] Error 100
make[1]: Leaving directory '/builds/software/ias/networking/vpp'
make: *** [Makefile:373: /builds/software/ias/networking/vpp/build-root/.deps.ok] Error 2

Type: fix
Change-Id: I057cebf5e31c0f3eef42f7ad07c7759a2d8e7f73
Signed-off-by: Jay Wang <[email protected]>