Remove unused imports which share prefixes.

Bug: dart-lang/sdk#38784
Change-Id: I2e64f0271ecbcaa7c791403f06e4e963a141b85b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/163662
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

Author: srawlins

pkg/front_end/lib/src/fasta/source/value_kinds.dart

@@ -14,32 +14,11 @@ import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' as type
 
 import 'package:kernel/ast.dart' as type;
 
-import '../builder/builder.dart' as type;
-import '../builder/builtin_type_declaration_builder.dart' as type;
-import '../builder/class_builder.dart' as type;
-import '../builder/constructor_reference_builder.dart' as type;
-import '../builder/dynamic_type_declaration_builder.dart' as type;
-import '../builder/enum_builder.dart' as type;
-import '../builder/field_builder.dart' as type;
 import '../builder/formal_parameter_builder.dart' as type;
-import '../builder/function_builder.dart' as type;
-import '../builder/function_type_builder.dart' as type;
-import '../builder/invalid_type_declaration_builder.dart' as type;
-import '../builder/library_builder.dart' as type;
-import '../builder/member_builder.dart' as type;
 import '../builder/metadata_builder.dart' as type;
-import '../builder/mixin_application_builder.dart' as type;
-import '../builder/modifier_builder.dart' as type;
-import '../builder/name_iterator.dart' as type;
-import '../builder/named_type_builder.dart' as type;
-import '../builder/nullability_builder.dart' as type;
-import '../builder/prefix_builder.dart' as type;
-import '../builder/type_alias_builder.dart' as type;
 import '../builder/type_builder.dart' as type;
-import '../builder/type_declaration_builder.dart' as type;
 import '../builder/type_variable_builder.dart' as type;
 import '../builder/unresolved_type.dart' as type;
-import '../builder/void_type_declaration_builder.dart' as type;
 
 import '../identifiers.dart' as type;