fix: avoid overlapping definition for T::Enum synthetic serialize() method

[chrapkowski-sg]

Removes the synthetic serialize() definition generation.

Motivation

When users click "Find References" on a T::Enum class name in Sourcegraph, the UI sometimes shows references to the serialize() method instead of references to the class itself.

This happens because scip-ruby emits two definitions at the exact same source location:

1. The class definition (e.g., Foo#)
2. The synthetic serialize() method (e.g., Foo#serialize().)

When the Sourcegraph frontend queries for the symbol at a position and finds multiple overlapping definitions, it may pick the wrong one, causing Find References to return incorrect results.

Now only definition for the class is provided:

Problem

The synthetic serialize() method definition was emitted at the T::Enum class
declaration location, causing overlapping definitions with the class itself.
This broke Find References in Sourcegraph UI, which would pick up serialize
references instead of class references.

Before

class Foo < T::Enum
#     ^^^ definition [..] Foo#
#     ^^^ definition [..] Foo#serialize().
#           ^ reference [..] T#
#              ^^^^ reference [..] Module#public().
#              ^^^^ reference [..] String#
#              ^^^^ reference [..] T#Enum#

After

class Foo < T::Enum
#     ^^^ definition [..] Foo#
#           ^ reference [..] T#
#              ^^^^ reference [..] T#Enum#

Test plan

See included automated tests.

[chrapkowski-sg]

This change is part of the following stack:

• Fix failing CI due to macos-13 deprecation #247
  • fix: avoid overlapping definition for T::Enum synthetic serialize() method #246 ◀

_{Change managed by git-spice.}