[GlobalISel][NFC]Delete the comments of XXLegalizerInfo (#76918)

Delete the LegalizerInfo comments of AArch64/AMD64/ARM/M68k/RISCV/x86,
they are copied from register bank.

Author: shining1984

llvm/lib/Target/AArch64/GISel/AArch64LegalizerInfo.h

@@ -23,7 +23,6 @@ namespace llvm {
 
 class AArch64Subtarget;
 
-/// This class provides the information for the target register banks.
 class AArch64LegalizerInfo : public LegalizerInfo {
 public:
   AArch64LegalizerInfo(const AArch64Subtarget &ST);

llvm/lib/Target/AMDGPU/AMDGPULegalizerInfo.h

@@ -27,7 +27,6 @@ class MachineIRBuilder;
 namespace AMDGPU {
 struct ImageDimIntrinsicInfo;
 }
-/// This class provides the information for the target register banks.
 class AMDGPULegalizerInfo final : public LegalizerInfo {
   const GCNSubtarget &ST;
 

llvm/lib/Target/ARM/ARMLegalizerInfo.h

@@ -23,7 +23,6 @@ namespace llvm {
 
 class ARMSubtarget;
 
-/// This class provides the information for the target register banks.
 class ARMLegalizerInfo : public LegalizerInfo {
 public:
   ARMLegalizerInfo(const ARMSubtarget &ST);

llvm/lib/Target/M68k/GISel/M68kLegalizerInfo.h

@@ -20,7 +20,6 @@ namespace llvm {
 
 class M68kSubtarget;
 
-/// This struct provides the information for the target register banks.
 struct M68kLegalizerInfo : public LegalizerInfo {
 public:
   M68kLegalizerInfo(const M68kSubtarget &ST);

llvm/lib/Target/RISCV/GISel/RISCVLegalizerInfo.h

@@ -21,7 +21,6 @@ class GISelChangeObserver;
 class MachineIRBuilder;
 class RISCVSubtarget;
 
-/// This class provides the information for the target register banks.
 class RISCVLegalizerInfo : public LegalizerInfo {
   const RISCVSubtarget &STI;
   const unsigned XLen;

llvm/lib/Target/X86/GISel/X86LegalizerInfo.h

@@ -21,7 +21,6 @@ namespace llvm {
 class X86Subtarget;
 class X86TargetMachine;
 
-/// This class provides the information for the target register banks.
 class X86LegalizerInfo : public LegalizerInfo {
 private:
   /// Keep a reference to the X86Subtarget around so that we can