[9.1](backport #45053) [Filebeat] Use existing constant for FIPS distribution

[mergify]

Proposed commit message

This PR is a follow up to #45036. In that PR, a new constant was introduced in libbeat, common.FIPSMode to determine if we're running a FIPS-capable distribution of a Beat or not. Turns out there was already such a constant in place, version.FIPSDistribution. So this PR here deletes common.FIPSMode and reuses version.FIPSDistribution instead.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

$ go test ./filebeat/input/v2/ -test.run TestLoader_ConfigureFIPS -test.count 1 -test.v
=== RUN   TestLoader_ConfigureFIPS
    loader_test.go:209: FIPS mode = false; err = <nil>
--- PASS: TestLoader_ConfigureFIPS (0.00s)
PASS
ok  	github.com/elastic/beats/v7/filebeat/input/v2	0.006s

In an environment configured for FIPS, i.e. with the Microsoft Go fork installed and with the OpenSSL FIPS provider installed:

$ GOEXPERIMENT=systemcrypto go test -tags requirefips ./filebeat/input/v2/ -test.run TestLoader_ConfigureFIPS -test.count 1 -test.v
=== RUN   TestLoader_ConfigureFIPS
    loader_test.go:209: FIPS mode = true; err = running a FIPS-capable distribution but input [a] is not FIPS capable
--- PASS: TestLoader_ConfigureFIPS (0.00s)
PASS
ok  	github.com/elastic/beats/v7/filebeat/input/v2	0.014s

---

This is an automatic backport of pull request #45053 done by [Mergify](https://mergify.com).

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