Remove deprecated notebooks from readme.

Author: kmoscoe

notebooks/README.md

@@ -15,8 +15,6 @@ Notebook | Description
 [`analyzing_genomic_data.ipynb`](https://colab.research.google.com/drive/1Io7EDr4LjfPLl_l2JYY8__WbfitfNlOf) | A notebook that analyzes genetic variants within RUNX1 (provided by multiple datasets from UCSC Genome Browser, NCBI/gene, and ClinVar).
 [`Drug_Discovery_With_Data_Commons.ipynb`](https://colab.research.google.com/drive/1dSKYiRMn3mbDsInorQzYM0yk7sqv6fIV) | A notebook performing drug discovery by identifying novel applications of previously approved drugs using Biomedical Data Commons.
 [`protein-charts.ipynb`](https://colab.research.google.com/drive/1Kh-ufqobdChZ2qQgEY0rdPA2_DBmOiSG) | A notebook summarizing various protein properties and interactions using graphical visualizations.
-[`Superfund sites (basic)`](Accessing_Superfund_data_from_Data_Commons.ipynb) | A notebook that illustrates basic access to [Superfund sites](https://en.wikipedia.org/wiki/List_of_Superfund_sites) data in Data Commons.
-[`Superfund sites (extended)`](Analyzing_SuperfundSites_with_Data_Commons.ipynb) | A notebook that includes extended analysis using [Superfund sites](https://en.wikipedia.org/wiki/List_of_Superfund_sites) data in Data Commons.
 
 ## Maintenance