Remove extraneous parentheses (#1274)

Fixes -Wparentheses-equality compiler warnings.

display/d.vect.thematic/display.c

@@ -74,7 +74,7 @@ int display_lines(struct Map_info *Map, struct cat_list *Clist,
             if (ltype == -1) {
                 G_fatal_error(_("Unable to read vector map"));
             }
-            else if ((ltype == -2)) {   /* EOF */
+            else if (ltype == -2) {   /* EOF */
                 break;
             }
         }

lib/vector/Vlib/merge_lines.c

@@ -138,7 +138,7 @@ int Vect_merge_lines(struct Map_info *Map, int type, int *new_lines,
 		curr_line = Vect_get_node_line(Map, next_node, i);
 		if ((Plus->Line[abs(curr_line)]->type & GV_LINES))
 		    lines_type++;
-		if ((Plus->Line[abs(curr_line)]->type == ltype)) {
+		if (Plus->Line[abs(curr_line)]->type == ltype) {
 		    if (abs(curr_line) != abs(first)) {
 			Vect_read_line(Map, NULL, Cats, abs(curr_line));
 			
@@ -186,7 +186,7 @@ int Vect_merge_lines(struct Map_info *Map, int type, int *new_lines,
 		curr_line = Vect_get_node_line(Map, next_node, i);
 		if ((Plus->Line[abs(curr_line)]->type & GV_LINES))
 		    lines_type++;
-		if ((Plus->Line[abs(curr_line)]->type == ltype)) {
+		if (Plus->Line[abs(curr_line)]->type == ltype) {
 		    if (abs(curr_line) != abs(last)) {
 			Vect_read_line(Map, NULL, Cats, abs(curr_line));