[StaticAnalyzer] Remove redundant declaration isStdSmartPtr (NFC)

An identical declaration is present just a couple of lines above the
line being removed in this patch.

Identified with readability-redundant-declaration.

Author: kazutakahirata

clang/lib/StaticAnalyzer/Checkers/SmartPtr.h

@@ -25,8 +25,6 @@ bool isStdSmartPtrCall(const CallEvent &Call);
 bool isStdSmartPtr(const CXXRecordDecl *RD);
 bool isStdSmartPtr(const Expr *E);
 
-bool isStdSmartPtr(const CXXRecordDecl *RD);
-
 /// Returns whether the smart pointer is null or not.
 bool isNullSmartPtr(const ProgramStateRef State, const MemRegion *ThisRegion);