Remove syntax distinction between builtin and user calls

c/testdata

@@ -133,21 +133,21 @@ null
 # Oh god.
 #
 
-def f: . + 1; def g: def g: . + 100; $$f | $$g | $$f; ($$f | $$g), $$g
+def f: . + 1; def g: def g: . + 100; f | g | f; (f | g), g
 3.0
 106.0
 105.0
 
-def f: (1000,2000); $$f
+def f: (1000,2000); f
 123412345
 1000
 2000
 
-[[20,10][1,0] as $x | def f: (100,200) as $y | def g: [$x + $y, .]; . + $x | $$g; $$f[0] | [$$f][0][1] | $$f]
+[[20,10][1,0] as $x | def f: (100,200) as $y | def g: [$x + $y, .]; . + $x | g; f[0] | [f][0][1] | f]
 "woo, testing!"
 [[110.0, 130.0], [210.0, 130.0], [110.0, 230.0], [210.0, 230.0], [120.0, 160.0], [220.0, 160.0], [120.0, 260.0], [220.0, 260.0]]
 
-def f(x): $$x | $$x; $$f([.], . + [42])
+def f(x): x | x; f([.], . + [42])
 [1,2,3]
 [[[1,2,3]]]
 [[1,2,3],42]