[Support] Remove redundant declaration setCurrentDebugTypes (NFC)

The function is declared in llvm/include/llvm/Support/Debug.h.

Identified with readability-redundant-declaration.

Author: kazutakahirata

llvm/lib/Support/Debug.cpp

@@ -61,12 +61,6 @@ bool isCurrentDebugType(const char *DebugType) {
   return false;
 }
 
-/// Set the current debug type, as if the -debug-only=X
-/// option were specified.  Note that DebugFlag also needs to be set to true for
-/// debug output to be produced.
-///
-void setCurrentDebugTypes(const char **Types, unsigned Count);
-
 void setCurrentDebugType(const char *Type) {
   setCurrentDebugTypes(&Type, 1);
 }