lexer.c: fix initialize function signature

Fix initialize function signature for Ruby 3.x compatibility where the
arity checks are enforced. This is done by removing unused input_text
parameter to match arity 0 declaration.

Fixes:

```
In file included from /usr/local/include/ruby-3.1.0/ruby/ruby.h:26,
                 from /usr/local/include/ruby-3.1.0/ruby.h:38,
                 from ../../../../ext/ios_parser/c_lexer/lexer.c:1:
../../../../ext/ios_parser/c_lexer/lexer.c: In function 'Init_c_lexer':
/usr/local/include/ruby-3.1.0/ruby/internal/anyargs.h:287:135: error: passing argument 3 of 'rb_define_method_00' from incompatible pointer type [-Wincompatible-pointer-types]
  287 | , mid, func, arity)           RBIMPL_ANYARGS_DISPATCH_rb_define_method((arity), (func))((klass), (mid), (func), (arity))
      |                                                                                                         ^~~~~~
      |                                                                                                         |
      |                                                                                                         VALUE (*)(VALUE,  VALUE) {aka long unsigned int (*)(long unsigned int,  long unsigned int)}

../../../../ext/ios_parser/c_lexer/lexer.c:610:5: note: in expansion of macro 'rb_define_method'
  610 |     rb_define_method(rb_cCLexer, "initialize", initialize, 0);
 /usr/local/include/ruby-3.1.0/ruby/internal/anyargs.h:276:21: note: expected 'VALUE (*)(VALUE)' {aka 'long unsigned int (*)(long unsigned int)'} but argument is of type 'VALUE (*)(VALUE,  VALUE)' {aka 'long unsigned int (*)(long unsigned int,  long unsigned int)'}
  276 | RBIMPL_ANYARGS_DECL(rb_define_method, VALUE, const char *)
      |                     ^~~~~~~~~~~~~~~~
/usr/local/include/ruby-3.1.0/ruby/internal/anyargs.h:254:41: note: in definition of macro 'RBIMPL_ANYARGS_DECL'
  254 | RBIMPL_ANYARGS_ATTRSET(sym) static void sym ## _00(__VA_ARGS__, VALUE(*)(VALUE), int); \
      |                                         ^~~
At top level:     |     ^~~~~~~~~~~~~~~~
```

Author: skrobul

ext/ios_parser/c_lexer/lexer.c

@@ -201,7 +201,7 @@ static VALUE allocate(VALUE klass) {
     return Data_Wrap_Struct(klass, mark, deallocate, lex);
 }
 
-static VALUE initialize(VALUE self, VALUE input_text) {
+static VALUE initialize(VALUE self) {
     LexInfo *lex;
     Data_Get_Struct(self, LexInfo, lex);