test-privserver: Move helper executable out of name-test/

This means we don't need to distinguish between DBUS_NAME_TEST_EXEC and
DBUS_TEST_EXEC any more, because all test helper executables are in the
same place, both during build and when installed (we don't install
test-privserver since no installed test requires it yet, but in
principle we could).

Signed-off-by: Simon McVittie <smcv@collabora.com>
12 jobs for all-helpers-in-test in 10 minutes and 1 second (queued for 4 seconds)
Status Job ID Name Coverage
  Build
manual #62444
allowed to fail manual
build:buster
passed #62438
build:cmake

00:03:17

passed #62435
build:debug

00:08:19

manual #62440
allowed to fail manual
build:i686-w64-mingw32-cmake
passed #62439
build:i686-w64-mingw32-debug

00:05:03

manual #62443
allowed to fail manual
build:jessie
manual #62437
allowed to fail manual
build:legacy
passed #62434
build:production

00:05:25

manual #62436
allowed to fail manual
build:reduced
passed #62441
build:x86_64-w64-mingw32

00:04:56

passed #62442
build:x86_64-w64-mingw32-cmake-debug

00:04:16

manual #62445
allowed to fail manual
build:xenial