[Ada] Code cleanup of alignment representation clauses in dispatch tables

[Ada] Code cleanup of alignment representation clauses in dispatch tables

This patch does not modify the functionality of the compiler; it avoids
generating non-required alignment representation clauses for dispatch
tables.

2019-09-18  Javier Miranda  <miranda@adacore.com>

gcc/ada/

	* exp_disp.adb (Make_DT, Make_Secondary_DT): Remove generation
	of alignment representation clause for the following tables:
	Predef_Prims, Iface_DT, TSD, ITable, DT.

From-SVN: r275853