Drop use of federated_learning::kFlocIdSortingLshBasedComputation

This definition has been dropped upstream as it's enabled by default
now, but even in that case that doesn't make a difference for Brave
as the FlocIdProviderImpl object is never created as per [1], so we
can simply drop these 2 lines.

[1] #8468

Chromium change:

https://chromium.googlesource.com/chromium/src.git/+/77462226d2aa2980c80e009ab7de098407af653d

commit 77462226d2aa2980c80e009ab7de098407af653d
Author: Yao Xiao <yaoxia@chromium.org>
Date:   Wed Mar 31 23:11:46 2021 +0000

    [floc] Use sorting-lsh by default. Remove base::Feature and clean up tests.

    Bug: 1190992

app/brave_main_delegate.cc

@@ -224,7 +224,6 @@ bool BraveMainDelegate::BasicStartupComplete(int* exit_code) {
     features::kWebOTP.name,
     federated_learning::kFederatedLearningOfCohorts.name,
     federated_learning::kFlocIdComputedEventLogging.name,
-    federated_learning::kFlocIdSortingLshBasedComputation.name,
     kSharingQRCodeGenerator.name,
     net::features::kFirstPartySets.name,
     network_time::kNetworkTimeServiceQuerying.name,

app/brave_main_delegate_browsertest.cc

@@ -81,7 +81,6 @@ IN_PROC_BROWSER_TEST_F(BraveMainDelegateBrowserTest, DisabledFeatures) {
       &features::kWebOTP,
       &federated_learning::kFederatedLearningOfCohorts,
       &federated_learning::kFlocIdComputedEventLogging,
-      &federated_learning::kFlocIdSortingLshBasedComputation,
       &kEnableProfilePickerOnStartupFeature,
       &kSharingQRCodeGenerator,
       &net::features::kFirstPartySets,