Revert "tree-sra: Avoid refreshing into const base decls (PR 100453)"

Revert "tree-sra: Avoid refreshing into const base decls (PR 100453)"

This reverts commit ca9bb74a5f856ccdceb4797f18b0a4ac8f49d069.
...because of Ada issues I did not catch with original testing.

gcc/ChangeLog:

2021-05-12  Martin Jambor  <mjambor@suse.cz>

	Revert:
        PR tree-optimization/100453
	* tree-sra.c (sra_modify_assign): All const base accesses do not
	need refreshing, not just those from decl_pool.
	(sra_modify_assign): Do not refresh into a const base decl.

gcc/testsuite/ChangeLog:

2021-05-12  Martin Jambor  <mjambor@suse.cz>

	Revert:
        PR tree-optimization/100453
	* gcc.dg/tree-ssa/pr100453.c: New test.