tab-switching: Re-enable tab_switching on linux.

Re-enable the tab-switching benchmark on linux after the tabs-metric fix
in crrev.com/c/1083790.

BUG=842732

Change-Id: Iac9ae2f83ccf6082bb3cf1e7223ccb89bf517f85
Reviewed-on: https://chromium-review.googlesource.com/1084056Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#564735}

tools/perf/expectations.config

@@ -348,7 +348,6 @@ crbug.com/843547 [ Android_Go ] system_health.memory_mobile/background:news:nyti
 
 # Benchmark: tab_switching.typical_25
 crbug.com/747026 [ Mac ] tab_switching.typical_25/multitab:misc:typical24 [ Skip ]
-crbug.com/842732 [ Linux ] tab_switching.typical_25/multitab:misc:typical24 [ Skip ]
 
 # Benchmark: thread_times.key_hit_test_cases
 crbug.com/750876 [ All ] thread_times.key_hit_test_cases/* [ Skip ]