tests: Use CALLS_PLUGIN_DIR to search for plugins in the build dir

There is no need to add a second variable to search for plugins, we can
use CALLS_PLUGIN_DIR directly.

plugins/provider/tests/meson.build

@@ -32,12 +32,12 @@ test_env = [
   'CALLS_AUDIOSRC=audiotestsrc',
   'CALLS_AUDIOSINK=fakesink',
   'GSETTINGS_SCHEMA_DIR=@0@/data'.format(meson.project_build_root()),
+  'CALLS_PLUGIN_DIR=@0@/plugins'.format(meson.project_build_root()),
 ]
 
 test_cflags = [
   '-DFOR_TESTING',
   '-Wno-error=deprecated-declarations',
-  '-DPLUGIN_BUILDDIR="@0@"'.format(full_calls_plugin_builddir),
 ]
 
 test_link_args = [

plugins/provider/tests/test-sip.c

@@ -429,10 +429,6 @@ main (int   argc,
   gtk_test_init (&argc, &argv, NULL);
 
   gst_init (NULL, NULL);
-
-#ifdef PLUGIN_BUILDDIR
-  peas_engine_add_search_path (peas_engine_get_default (), PLUGIN_BUILDDIR, NULL);
-#endif
   /* this is a workaround for an issue with sofia: https://github.com/freeswitch/sofia-sip/issues/58 */
   su_random64 ();