[FIR] get rid of FirFileAnnotationsContainer

This element has been introduced to simplify resolution logic in LL FIR,
but now this element is redundant and only complicates the code as after
KT-56683 `FirFile` has real phases

^KT-65876 Fixed

analysis/low-level-api-fir/testData/getOrBuildFir/annotations/fileAnnotationScript.txt

@@ -8,7 +8,6 @@ FIR element rendered:
 FIR FILE:
 FILE: [ResolvedTo(ANNOTATION_ARGUMENTS)] fileAnnotationScript.kts
     @FILE:R|kotlin/Suppress|[Types](names = vararg(String()))
-    [ResolvedTo(ANNOTATION_ARGUMENTS)] annotations container
     context(<script>@kotlin.script.templates.standard.ScriptTemplateWithArgs)
     SCRIPT: [ResolvedTo(RAW_FIR)] <script-fileAnnotationScript.kts>
         [ResolvedTo(RAW_FIR)] lval args: R|kotlin/Array<kotlin/String>|