[IR] Remove redundant declarations (NFC) (llvm#166084)

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/IR/ModuleSummaryIndex.cpp

@@ -34,8 +34,6 @@ static cl::opt<bool> ImportConstantsWithRefs(
     "import-constants-with-refs", cl::init(true), cl::Hidden,
     cl::desc("Import constant global variables with references"));
 
-constexpr uint32_t FunctionSummary::ParamAccess::RangeWidth;
-
 FunctionSummary FunctionSummary::ExternalNode =
     FunctionSummary::makeDummyFunctionSummary(
         SmallVector<FunctionSummary::EdgeTy, 0>());
@@ -88,8 +86,6 @@ std::pair<unsigned, unsigned> FunctionSummary::specialRefCounts() const {
   return {RORefCnt, WORefCnt};
 }
 
-constexpr uint64_t ModuleSummaryIndex::BitcodeSummaryVersion;
-
 uint64_t ModuleSummaryIndex::getFlags() const {
   uint64_t Flags = 0;
   // Flags & 0x4 is reserved. DO NOT REUSE.