Revert "[llvm-exegesis] Add benchmark latency option on X86 that uses LBR for more precise measurements."
From @erichkeane:
```
This patch doesn't seem to build for me:
/iusers/ekeane1/workspaces/llvm-project/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp: In function ‘llvm::Error llvm::exegesis::parseDataBuffer(const char*, size_t, const void*, const void*, llvm::SmallVector<long int, 4>*)’:
/iusers/ekeane1/workspaces/llvm-project/llvm/tools/llvm-exegesis/lib/X86/X86Counter.cpp:99:37: error: ‘struct perf_branch_entry’ has no member named ‘cycles’
CycleArray->push_back(Entry.cycles);
I'm on RHEL7, so I have kernel 3.10, so it doesn't have 'cycles'.
According ot this: https://elixir.bootlin.com/linux/v4.3/source/include/uapi/linux/perf_event.h#L963 kernel 4.3 is the first time that 'cycles' appeared in this structure.
```
diff --git a/llvm/docs/CommandGuide/llvm-exegesis.rst b/llvm/docs/CommandGuide/llvm-exegesis.rst
index f3bce16..321cdf5 100644
--- a/llvm/docs/CommandGuide/llvm-exegesis.rst
+++ b/llvm/docs/CommandGuide/llvm-exegesis.rst
@@ -192,24 +192,10 @@
.. option:: -mode=[latency|uops|inverse_throughput|analysis]
- Specify the run mode. Note that some modes have additional requirements and options.
+ Specify the run mode. Note that if you pick `analysis` mode, you also need
+ to specify at least one of the `-analysis-clusters-output-file=` and
+ `-analysis-inconsistencies-output-file=`.
- `latency` mode can be make use of either RDTSC or LBR.
- `latency[LBR]` is only available on X86 (at least `Skylake`).
- To run in this mode, a positive value must be specified for `x86-lbr-sample-period` and `--repetition-mode=loop`
-
- In `analysis` mode, you also need to specify at least one of the
- `-analysis-clusters-output-file=` and `-analysis-inconsistencies-output-file=`.
-
-.. option:: -x86-lbr-sample-period=<nBranches/sample>
-
- Specify the LBR sampling period - how many branches before we take a sample.
- When a positive value is specified for this option and when the mode is `latency`,
- we will use LBRs for measuring.
- On choosing the "right" sampling period, a small value is preferred, but throttling
- could occur if the sampling is too frequent. A prime number should be used to
- avoid consistently skipping certain blocks.
-
.. option:: -repetition-mode=[duplicate|loop|min]
Specify the repetition mode. `duplicate` will create a large, straight line