fix(dashboard): avoid duplicated toast component

[stephenLYZ]

SUMMARY

This PR fixes the explore toast that will render twice when going to the dashboard. Essentially, toast has two identical components in the dashboard, it will be rendered twice.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

before

2021-06-13.5.55.30.mov

components:

after

2021-06-13.5.54.27.mov

components:

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue: [dashboard]Toasts when saving/adding to dashboard are duplicated and get overlaid on themselves #15099
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

Merging #15138 (0b16956) into master (4289929) will increase coverage by 0.08%.
The diff coverage is n/a.

❗ Current head 0b16956 differs from pull request most recent head d3f2fad. Consider uploading reports for the commit d3f2fad to get more accurate results

@@            Coverage Diff             @@
##           master   #15138      +/-   ##
==========================================
+ Coverage   77.33%   77.41%   +0.08%     
==========================================
  Files         969      969              
  Lines       50070    49917     -153     
  Branches     6439     6393      -46     
==========================================
- Hits        38722    38644      -78     
+ Misses      11143    11070      -73     
+ Partials      205      203       -2     

Flag	Coverage Δ
javascript	72.21% <ø> (+0.13%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...d/components/DashboardBuilder/DashboardBuilder.tsx	90.90% <ø> (+1.43%)	⬆️
.../src/dashboard/components/gridComponents/Chart.jsx	81.18% <0.00%> (-3.86%)	⬇️
...rontend/src/SqlLab/components/SqlEditorLeftBar.jsx	53.22% <0.00%> (-2.84%)	⬇️
...tiveFilters/FilterBar/FilterSets/FiltersHeader.tsx	91.66% <0.00%> (-1.36%)	⬇️
...c/filters/components/Select/SelectFilterPlugin.tsx	79.04% <0.00%> (-1.14%)	⬇️
...omponents/nativeFilters/FilterBar/Header/index.tsx	90.90% <0.00%> (-0.99%)	⬇️
superset/utils/webdriver.py	78.08% <0.00%> (-0.59%)	⬇️
superset/databases/api.py	92.77% <0.00%> (-0.42%)	⬇️
superset/connectors/base/models.py	88.37% <0.00%> (-0.34%)	⬇️
...tersConfigModal/FiltersConfigForm/ColumnSelect.tsx	97.14% <0.00%> (-0.23%)	⬇️
... and 32 more

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[villebro]

@stephenLYZ this needs a rebase

[villebro]

LGTM