doc: update presym documentation

Remove references to conf.disable_presym and MRB_NO_PRESYM.

Co-authored-by: Claude <noreply@anthropic.com>

doc/guides/compile.md

@@ -261,12 +261,9 @@ end
 
 ### Preallocated Symbols
 
-By far, preallocated symbols are highly compatible with the previous versions, so
-we expect you won't see any problem with them. But just in case you face any
-issue, you can disable preallocated symbols by specifying `conf.disable_presym`.
-
-In the build process, `mrbc` under cross compiling environment will be compiled
-with this configuration.
+Preallocated symbols are always enabled. Symbol IDs used in C source code
+(via `MRB_SYM()` etc.) are resolved to compile-time constants during the
+build process.
 
 ### Mrbgems
 

doc/guides/symbol.md

@@ -73,14 +73,6 @@ For `MRB_OPSYM()`, specify the names corresponding to operators (see
 can be specified for it). Other than that, describe only word characters
 excluding leading and ending punctuation.
 
-These macros are converted to static symbol IDs at compile time, unless
-preallocate symbols are disabled by `conf.disable_presym`. In that case,
-these macros are expanded to `mrb_intern_lit` calls, therefore the mruby state
-variable is required. The above macros assume the variable name is `mrb`. If
-its name is not `mrb`, you need to use macros with `_2` suffix, such as
-`MRB_SYM_2` to specify `mrb_state*` variable.
-
-### Disabling Preallocated Symbols
-
-You can disable preallocated symbols by specifying `conf.disable_presym` in the
-configuration file.
+These macros are converted to static symbol IDs at compile time.
+The `_2` suffix variants (e.g., `MRB_SYM_2`) accept an explicit
+`mrb_state*` parameter but currently ignore it.