MEDIUM: stick-table: remove the now duplicate find_stktable() function

Since proxy_tbl_by_name() already does the same job, let's not keep
duplicate functions and use this one only.
diff --git a/src/sample.c b/src/sample.c
index 3ad2d20..47d48c8 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -1214,7 +1214,7 @@
 		case ARGT_TAB:
 			if (arg->data.str.len) {
 				pname = arg->data.str.str;
-				px = find_stktable(pname);
+				px = proxy_tbl_by_name(pname);
 			}
 
 			if (!px) {