tools: Remove unused PluginLoader includes

As far as I can tell there are 2 parallel plugin mechanisms.
opt -load=plugin does not work, and is ignored. opt -load-pass-plugin
does work. The only user of PluginLoader appears to be bugpoint.

Author: arsenm

clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp

@@ -22,7 +22,6 @@
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InitLLVM.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"

lld/tools/lld/lld.cpp

@@ -35,7 +35,6 @@
 #include "llvm/Support/CrashRecoveryContext.h"
 #include "llvm/Support/LLVMDriver.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/Process.h"
 #include "llvm/TargetParser/Host.h"
 #include "llvm/TargetParser/Triple.h"

llvm/tools/llc/llc.cpp

@@ -44,7 +44,6 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/FormattedStream.h"
 #include "llvm/Support/InitLLVM.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/TimeProfiler.h"

llvm/tools/lli/lli.cpp

@@ -59,7 +59,6 @@
 #include "llvm/Support/Memory.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/SourceMgr.h"

llvm/tools/llvm-lto2/llvm-lto2.cpp

@@ -25,7 +25,6 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/InitLLVM.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/Threading.h"
 #include <atomic>

llvm/tools/opt/optdriver.cpp

@@ -43,7 +43,6 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/InitLLVM.h"
-#include "llvm/Support/PluginLoader.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/SystemUtils.h"
 #include "llvm/Support/TargetSelect.h"