[Ada] Fix deleted Compile_Time warnings causing crashes

[Pierre-Marie de Rodat]

Count_Compile_Time_Pragma_Warnings also counted deleted pragmas. This
caused discrepancies ultimately leading to a crash when Compile_Time
warnings were suppressed by a Warnings(Off, ...) pragma.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* erroutc.adb (Count_Compile_Time_Pragma_Warnings): Don't count
	deleted warnings.
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