tests: make functions static in test_uri.c

Fixes:

      CC       test_uri.o
    /home/smarchi/src/lttng-tools/tests/unit/test_uri.c:33:6: error: no previous declaration for ‘test_uri_parsing’ [-Werror=missing-declarations]
     void test_uri_parsing(void)
          ^~~~~~~~~~~~~~~~
    /home/smarchi/src/lttng-tools/tests/unit/test_uri.c:201:6: error: no previous declaration for ‘test_uri_cmp’ [-Werror=missing-declarations]
     void test_uri_cmp()
          ^~~~~~~~~~~~

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Change-Id: Ia0d7b08a10ec9f8d3f6f2d5b4fa9c4f417827024
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>