Remove unused Endian.h includes, NFC

Mainly avoids including Host.h everywhere:

$ diff -u <(sort thedeps-before.txt) <(sort thedeps-after.txt) \
    | grep '^[-+] ' | sort | uniq -c | sort -nr
   3141 - /usr/local/google/home/rnk/llvm-project/llvm/include/llvm/Support/Host.h

include/llvm/Support/Endian.h

@@ -13,9 +13,7 @@
 #ifndef LLVM_SUPPORT_ENDIAN_H
 #define LLVM_SUPPORT_ENDIAN_H
 
-#include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
-#include "llvm/Support/Host.h"
 #include "llvm/Support/SwapByteOrder.h"
 #include <cassert>
 #include <cstddef>

tools/llvm-ar/llvm-ar.cpp

@@ -26,6 +26,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/FormatVariadic.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"

tools/llvm-exegesis/lib/LlvmState.cpp

@@ -13,6 +13,7 @@
 #include "llvm/MC/MCContext.h"
 #include "llvm/MC/MCFixup.h"
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"

tools/llvm-objcopy/llvm-objcopy.cpp

@@ -35,6 +35,7 @@
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/Memory.h"
 #include "llvm/Support/Path.h"

unittests/Support/CommandLineTest.cpp

@@ -14,6 +14,7 @@
 #include "llvm/Config/config.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"