remove unnecessary reference

doc/references.rst

@@ -18,7 +18,6 @@ References
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-
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                      Residue depth: a novel parameter for the analysis of 
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@@ -47,9 +46,6 @@ References
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-.. [lovell2000] Lovell SC, Word JM, Richardson JS, Richardson DC (2000). 
-                The penultimate rotamer library. Proteins.
-
 .. [shapovalov2011] Shapovalov MV and Dunbrack RL Jr. (2011). 
                     A smoothed backbone-dependent rotamer library for proteins 
                     derived from adaptive kernel density estimates and 
@@ -59,7 +55,6 @@ References
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