[Ada] Minor cleanup in translation of calls to subprograms
gcc/ada/
* gcc-interface/ada-tree.h (DECL_STUBBED_P): Delete.
* gcc-interface/decl.c (gnat_to_gnu_entity): Do not set it.
* gcc-interface/trans.c (Call_to_gnu): Use GNAT_NAME local variable
and adjust accordingly. Replace test on DECL_STUBBED_P with direct
test on Convention and move it down in the processing.