[cleanup] Remove unused FLAG_print_builtin_scopes

Removing the 'native' flag from ParseInfo removed the last use-site
of this flag.

R=jgruber@chromium.org

Bug: v8:9043
Change-Id: I0e28d77c571c25c7925e8e372e631a9630492c25
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1550705Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60700}

src/flag-definitions.h

@@ -1286,7 +1286,6 @@ DEFINE_BOOL(print_ast, false, "print source AST")
 DEFINE_BOOL(trap_on_abort, false, "replace aborts by breakpoints")
 
 // compiler.cc
-DEFINE_BOOL(print_builtin_scopes, false, "print scopes for builtins")
 DEFINE_BOOL(print_scopes, false, "print scopes")
 
 // contexts.cc