[Support] Remove redundant declarations (NFC) (#166011)

In C++17, static constexpr members are implicitly inline, so they no
longer require an out-of-line definition.

Identified with readability-redundant-declaration.

Author: kazutakahirata

llvm/lib/Support/raw_ostream.cpp

@@ -61,17 +61,6 @@
 
 using namespace llvm;
 
-constexpr raw_ostream::Colors raw_ostream::BLACK;
-constexpr raw_ostream::Colors raw_ostream::RED;
-constexpr raw_ostream::Colors raw_ostream::GREEN;
-constexpr raw_ostream::Colors raw_ostream::YELLOW;
-constexpr raw_ostream::Colors raw_ostream::BLUE;
-constexpr raw_ostream::Colors raw_ostream::MAGENTA;
-constexpr raw_ostream::Colors raw_ostream::CYAN;
-constexpr raw_ostream::Colors raw_ostream::WHITE;
-constexpr raw_ostream::Colors raw_ostream::SAVEDCOLOR;
-constexpr raw_ostream::Colors raw_ostream::RESET;
-
 raw_ostream::~raw_ostream() {
   // raw_ostream's subclasses should take care to flush the buffer
   // in their destructors.