[FIR] Drop isStatic field from FirJavaFieldBuilder

It is not used anywhere, and it looks like the proper way to set
`isStatic` is through the `status` field.

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/FirJavaFacade.kt

@@ -540,7 +540,6 @@ abstract class FirJavaFacade(
                 modality = javaField.modality
                 returnTypeRef = returnType.toFirJavaTypeRef(session)
                 isVar = !javaField.isFinal
-                isStatic = javaField.isStatic
                 annotationBuilder = { javaField.convertAnnotationsToFir(session) }
 
                 lazyInitializer = lazy {

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/declarations/FirJavaField.kt

@@ -178,7 +178,6 @@ class FirJavaField @FirImplementationDetail constructor(
 internal class FirJavaFieldBuilder : FirFieldBuilder() {
     var modality: Modality? = null
     lateinit var visibility: Visibility
-    var isStatic: Boolean by Delegates.notNull()
     var isFromSource: Boolean by Delegates.notNull()
     lateinit var annotationBuilder: () -> List<FirAnnotation>
     var lazyInitializer: Lazy<FirExpression?>? = null

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/enhancement/SignatureEnhancement.kt

@@ -132,7 +132,6 @@ class FirSignatureEnhancement(
                     visibility = firElement.visibility
                     modality = firElement.modality
                     isVar = firElement.isVar
-                    isStatic = firElement.isStatic
                     annotationBuilder = { firElement.annotations }
                     status = firElement.status
                     if (firElement is FirJavaField) {