Verify blazemark_kernels flag is unused and remove

https://github.com/GoogleCloudPlatform/PerfKitBenchmarker/blob/561e4cc9295e9b5f109cc98dc824e9663447d1f3/perfkitbenchmarker/linux_benchmarks/blazemark_benchmark.py#L29
```
flags.DEFINE_list('blazemark_kernels', ['-only-blaze'], 'A list of additional '
'flags send to blazemark, in order to '
'enable/disable kernels/libraries. '
'Currently only support blaze. '
'See following link for more details: '
'https://bitbucket.org/blaze-lib/blaze/wiki/'
'Blazemark#!command-line-parameters')
```