[FIR] Remove FirLambdaArgumentExpression

It's not really necessary if the information about if the lambda was a
trailing lambda can be directly saved in FirAnonymousFunctionExpression.

Removing the FIR node uncovered a couple of bugs
(UNINITIALIZED_ENUM_ENTRY, ERROR_IN_CONTRACT_DESCRIPTION) that were
caused by assuming that a lambda is always a trailing lambda.

#KT-66124

compiler/fir/dump/src/org/jetbrains/kotlin/fir/dump/HtmlFirDump.kt

@@ -1573,11 +1573,6 @@ class HtmlFirDump internal constructor(private var linkResolver: FirLinkResolver
                     generate(expression.expression)
 
                 }
-                is FirLambdaArgumentExpression -> {
-                    keyword("lambda")
-                    +" = "
-                    generate(expression.expression)
-                }
                 is FirTypeOperatorCall -> generate(expression)
                 is FirEqualityOperatorCall -> generate(expression)
                 is FirBinaryLogicExpression -> generate(expression)