Remove undocumented method #to_c

Author: ksss

core/float.rbs

@@ -877,8 +877,6 @@ class Float < Numeric
           | (?by: Numeric, ?to: Numeric) { (Float) -> void } -> self
           | (?by: Numeric, ?to: Numeric) -> Enumerator[Float, self]
 
-  def to_c: () -> Complex
-
   # <!--
   #   rdoc-file=numeric.rb
   #   - to_f -> self

core/integer.rbs

@@ -1195,8 +1195,6 @@ class Integer < Numeric
   def times: () { (Integer) -> void } -> self
            | () -> ::Enumerator[Integer, self]
 
-  def to_c: () -> Complex
-
   # <!--
   #   rdoc-file=numeric.c
   #   - to_f -> float

core/rational.rbs

@@ -405,8 +405,6 @@ class Rational < Numeric
           | (?by: Numeric, ?to: Numeric) { (Rational) -> void } -> self
           | (?by: Numeric, ?to: Numeric) -> Enumerator[Rational, self]
 
-  def to_c: () -> Complex
-
   # <!--
   #   rdoc-file=rational.c
   #   - rat.to_f  ->  float

test/stdlib/Numeric_test.rb

@@ -33,4 +33,10 @@ def test_abs2
     assert_send_type '() -> Float', 1.0, :abs2
     assert_send_type '() -> Rational', 1r, :abs2
   end
+
+  def test_to_c
+    assert_send_type '() -> Complex', 1, :to_c
+    assert_send_type '() -> Complex', 1.0, :to_c
+    assert_send_type '() -> Complex', 1r, :to_c
+  end
 end