[llvm][docs] Update old metadata syntax in examples

[paulkirth]

Summary

This patch updates examples in the documentation to match the existing
convention. Calls to intrinsics that have metadata arguments were not
included.

[dexonsmith]

LGTM

llvm/docs/BlockFrequencyTerminology.rst

 .. code-block:: llvm
 
    define void @foo() {
        ; ...
        A:
            br i1 %cond, label %B, label %C, !prof !0
        ; ...
    }
-   !0 = metadata !{metadata !"branch_weights", i32 7, i32 8}
+   !0 = !{!"branch_weights", i32 7, i32 8}
 
 and this simple graph representation::
 
    A -> B  (edge-weight: 7)
    A -> C  (edge-weight: 8)
 
 The probability of branching from block A to block B is 7/15, and the
 probability of branching from block A to block C is 8/15.

llvm/docs/BranchWeightMetadata.rst

 ``BranchInst``
 ^^^^^^^^^^^^^^
 
 Metadata is only assigned to the conditional branches. There are two extra
 operands for the true and the false branch.
 
 .. code-block:: none
 
-  !0 = metadata !{
-    metadata !"branch_weights",
+  !0 = !{
+    !"branch_weights",
     i32 <TRUE_BRANCH_WEIGHT>,
     i32 <FALSE_BRANCH_WEIGHT>
   }
 
 ``SwitchInst``
 ^^^^^^^^^^^^^^
 
 Branch weights are assigned to every case (including the ``default`` case which
 is always case #0).
 
 .. code-block:: none
 
-  !0 = metadata !{
-    metadata !"branch_weights",
+  !0 = !{
+    !"branch_weights",
     i32 <DEFAULT_BRANCH_WEIGHT>
     [ , i32 <CASE_BRANCH_WEIGHT> ... ]
   }
 
 ``IndirectBrInst``
 ^^^^^^^^^^^^^^^^^^
 
 Branch weights are assigned to every destination.
 
 .. code-block:: none
 
-  !0 = metadata !{
-    metadata !"branch_weights",
+  !0 = !{
+    !"branch_weights",
     i32 <LABEL_BRANCH_WEIGHT>
     [ , i32 <LABEL_BRANCH_WEIGHT> ... ]
   }
 
 ``CallInst``
 ^^^^^^^^^^^^^^^^^^
 
 Calls may have branch weight metadata, containing the execution count of
 the call. It is currently used in SamplePGO mode only, to augment the
 block and entry counts which may not be accurate with sampling.
 
 .. code-block:: none
 
-  !0 = metadata !{
-    metadata !"branch_weights",
+  !0 = !{
+    !"branch_weights",
     i32 <CALL_BRANCH_WEIGHT>
   }
 
 ``InvokeInst``
 ^^^^^^^^^^^^^^^^^^
 
 Invoke instruction may have branch weight metadata with one or two weights.
 The second weight is optional and corresponds to the unwind branch.
 If only one weight is set then it contains the execution count of the call
 and used in SamplePGO mode only as described for the call instruction. If both
 weights are specified then the second weight contains count of unwind branch
 taken and the first weights contains the execution count of the call minus
 the count of unwind branch taken. Both weights specified are used to calculate
 BranchProbability as for BranchInst and for SamplePGO the sum of both weights
 is used.
 
 .. code-block:: none
 
-  !0 = metadata !{
-    metadata !"branch_weights",
+  !0 = !{
+    !"branch_weights",
     i32 <INVOKE_NORMAL_WEIGHT>
     [ , i32 <INVOKE_UNWIND_WEIGHT> ]
   }
 
 Other
 ^^^^^
 
 Other terminator instructions are not allowed to contain Branch Weight Metadata.