Remove redundant grammar symbols

access_method, database_name, and index_name are all just name, and
they are not used consistently for their alleged purpose, so remove
them.  They have been around since ancient times but have no current
reason for existing.  Removing them can simplify future grammar
refactoring.

Discussion: https://www.postgresql.org/message-id/flat/163c00a5-f634-ca52-fc7c-0e53deda8735%402ndquadrant.com

src/interfaces/ecpg/preproc/ecpg.trailer

@@ -114,7 +114,7 @@ connection_target: opt_database_name opt_server opt_port
 		}
 		;
 
-opt_database_name: database_name		{ $$ = $1; }
+opt_database_name: name				{ $$ = $1; }
 		| /*EMPTY*/			{ $$ = EMPTY; }
 		;
 
@@ -962,7 +962,7 @@ dis_name: connection_object			{ $$ = $1; }
 		| /* EMPTY */			{ $$ = mm_strdup("\"CURRENT\""); }
 		;
 
-connection_object: database_name		{ $$ = make3_str(mm_strdup("\""), $1, mm_strdup("\"")); }
+connection_object: name				{ $$ = make3_str(mm_strdup("\""), $1, mm_strdup("\"")); }
 		| DEFAULT			{ $$ = mm_strdup("\"DEFAULT\""); }
 		| char_variable			{ $$ = $1; }
 		;