Revert keeping of underscores between digits in camelize, closes #10995

Author: josevalim

lib/elixir/lib/macro.ex

@@ -1735,9 +1735,6 @@ defmodule Macro do
   defp do_camelize(<<?_, h, t::binary>>) when h >= ?a and h <= ?z,
     do: <<to_upper_char(h)>> <> do_camelize(t)
 
-  defp do_camelize(<<p, ?_, h, t::binary>>) when p >= ?0 and p <= ?9 and h >= ?0 and h <= ?9,
-    do: <<p, ?_, h>> <> do_camelize(t)
-
   defp do_camelize(<<?_, h, t::binary>>) when h >= ?0 and h <= ?9, do: <<h>> <> do_camelize(t)
   defp do_camelize(<<?_>>), do: <<>>
   defp do_camelize(<<?/, t::binary>>), do: <<?.>> <> camelize(t)

lib/elixir/test/elixir/macro_test.exs

@@ -1036,7 +1036,8 @@ defmodule MacroTest do
     assert Macro.camelize("foo__bar") == "FooBar"
     assert Macro.camelize("foo/bar") == "Foo.Bar"
     assert Macro.camelize("Foo.Bar") == "Foo.Bar"
-    assert Macro.camelize("foo1_0") == "Foo1_0"
+    assert Macro.camelize("foo1_0") == "Foo10"
+    assert Macro.camelize("foo_123_4_567") == "Foo1234567"
     assert Macro.camelize("FOO_BAR") == "FOO_BAR"
     assert Macro.camelize("FOO.BAR") == "FOO.BAR"
     assert Macro.camelize("") == ""