gh-106656: Remove --emit-line-directives from regen-cases (#106657)

If you prefer to see `#line` directives in generated_cases.c.h, run
```
make regen-cases CASESFLAG=-l
```
But please don't commit the result.

Makefile.pre.in

@@ -1543,10 +1543,11 @@ regen-opcode-targets:
 .PHONY: regen-cases
 regen-cases:
 	# Regenerate various files from Python/bytecodes.c
+	# Pass CASESFLAG=-l to insert #line directives in the output
 	PYTHONPATH=$(srcdir)/Tools/cases_generator \
 	$(PYTHON_FOR_REGEN) \
 	    $(srcdir)/Tools/cases_generator/generate_cases.py \
-		--emit-line-directives \
+		$(CASESFLAG) \
 		-o $(srcdir)/Python/generated_cases.c.h.new \
 		-m $(srcdir)/Include/internal/pycore_opcode_metadata.h.new \
 		-e $(srcdir)/Python/executor_cases.c.h.new \