Improve developer experience with ebpf testdata

I noticed that the git submodule in `ebpf/testdata`, will always be marked changed when you are on a case-insensitive file system/volume:

```
on a case-insensitive filesystem) and only one from the same
colliding group is in the working tree:

'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_DSCP.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_dscp.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_HL.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_hl.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_RATEEST.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_rateest.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_TCPMSS.ko'
'qemu_img/amd64/modules_extra/5.10.205-195.807.amzn2.x86_64/kernel/net/netfilter/xt_tcpmss.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_DSCP.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_dscp.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_HL.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_hl.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_RATEEST.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_rateest.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_TCPMSS.ko'
'qemu_img/arm64/modules_extra/5.10.205-195.807.amzn2.aarch64/kernel/net/netfilter/xt_tcpmss.ko'
```

See wrong fix and discussion in #3254 and upsteam https://github.com/pyroscope-io/pyroscope-ebpf-testdata/pull/4

Workaround (which is not ideally, as every new contributor has to run it):

```
$ git update-index --assume-unchanged ebpf/testdata
```

I wonder what the best way forward:

* Just remove the extra lowercase modules, I am fairly sure those modules are not touched by eBPF tests
* Ship testdata separately from git: Maybe a public object store bucket or using them from a docker image.

cc @aleks-p @korniltsev