Remove --harmony-modules flag and let embedder decide when modules are used

test/mjsunit/harmony/module-parsing-eval.js

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-// Flags: --harmony-modules
-
 // Check that import/export declarations are rejected in eval or local scope.
 assertThrows("export let x;", SyntaxError);
 assertThrows("import x from 'http://url';", SyntaxError);
 
 assertThrows("{ export let x; }", SyntaxError);
 assertThrows("{ import x from 'http://url'; }", SyntaxError);
 
 assertThrows("function f() { export let x; }", SyntaxError);
 assertThrows("function f() { import x from 'http://url'; }", SyntaxError);
 
 assertThrows("function f() { { export let x; } }", SyntaxError);
 assertThrows("function f() { { import x from 'http://url'; } }", SyntaxError);