Remove CallFrame.to_string

The desired string format for a CallFrame may differ between
applications using it. Inko itself does not use CallFrame.to_string
either, so let's just get rid of it.

runtime/src/std/debug.inko

@@ -2,7 +2,6 @@
 #
 # This module provides various facilities for debugging programs during
 # runtime, such as obtaining stack traces.
-import std::conversion::ToString
 import std::fs::path::(Path, ToPath)
 import std::string_buffer::StringBuffer
 
@@ -39,21 +38,6 @@ object CallFrame {
   }
 }
 
-impl ToString for CallFrame {
-  # Formats the CallFrame as a String
-  def to_string -> String {
-    let buffer = StringBuffer.new(
-      @path.to_string.inspect,
-      ', line ',
-      @line.to_string,
-      ', in ',
-      @name.inspect,
-    )
-
-    buffer.to_string
-  }
-}
-
 # Returns a stack trace leading up to the line that called this method.
 #
 # The stack trace is returned in reverse order. This means that the most recent

runtime/tests/test/std/test_debug.inko

@@ -27,14 +27,6 @@ test.group('std::debug::CallFrame.line') do (g) {
   }
 }
 
-test.group('std::debug::CallFrame.to_string') do (g) {
-  g.test('Converting a CallFrame to a String') {
-    let frame = CallFrame.new(path: 'foo.inko', name: 'foo', line: 1)
-
-    assert.equal(frame.to_string, '"foo.inko", line 1, in "foo"')
-  }
-}
-
 test.group('std::debug.stacktrace') do (g) {
   g.test('Obtaining a stacktrace to the caller') {
     let trace = debug.stacktrace
@@ -43,7 +35,7 @@ test.group('std::debug.stacktrace') do (g) {
 
     assert.true(trace.length > 0)
     assert.equal(last.name, '<block>')
-    assert.equal(last.line, 40)
+    assert.equal(last.line, 32)
     assert.equal(last.path, mirror.path)
   }
 
@@ -69,6 +61,6 @@ test.group('std::debug.last_call_frame_in') do (g) {
 
     assert.equal(frame.name, '<block>')
     assert.equal(frame.path, mirror.path)
-    assert.equal(frame.line, 68)
+    assert.equal(frame.line, 60)
   }
 }