Roll Harfbuzz to 2.7.0 (c6ca30dc757ff86416d97d358f20080b979b80c9) (flutter#20411)

* Roll Harfbuzz to 2.7.0 c6ca30dc757ff86416d97d358f20080b979b80c9 (HAVE_PTHREAD)

Author: dnfield

DEPS

@@ -125,7 +125,7 @@ deps = {
    Var('fuchsia_git') + '/third_party/rapidjson' + '@' + 'ef3564c5c8824989393b87df25355baf35ff544b',
 
   'src/third_party/harfbuzz':
-   Var('fuchsia_git') + '/third_party/harfbuzz' + '@' + 'f5c000538699a4e40649508a44f41d37035e6c35',
+   Var('fuchsia_git') + '/third_party/harfbuzz' + '@' + 'c6ca30dc757ff86416d97d358f20080b979b80c9',
 
   'src/third_party/libcxx':
    Var('fuchsia_git') + '/third_party/libcxx' + '@' + '7524ef50093a376f334a62a7e5cebf5d238d4c99',