[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/contextCollector/fileAnnotation.txt

@@ -14,7 +14,6 @@ Tower Data Context:
 
 FILE: [ResolvedTo(IMPORTS)] fileAnnotation.kt
     @FILE:Anno[Unresolved]()
-    [ResolvedTo(RAW_FIR)] annotations container
     @Target[Unresolved](LAZY_EXPRESSION) public final? [ResolvedTo(RAW_FIR)] annotation class Anno : R|kotlin/Annotation| {
         public? [ResolvedTo(RAW_FIR)] constructor(): R|Anno| {
             LAZY_super<R|kotlin/Any|>