modify bug : clean cache in Alluxio due to unknown linux release version

[haoeeeee]

Ⅰ. Describe what this PR does
When we clean cache with a preset timeout of 60s, we use command " timeout 60 alluxio fs free -f path".
Delete the judgment logic for judging different linux release versions

Ⅱ. Does this pull request fix one issue?
Fixes #1476

[codecov]

Codecov Report

Merging #1487 (cfa91c4) into master (2727bc7) will increase coverage by 0.20%.
The diff coverage is 100.00%.

❗ Current head cfa91c4 differs from pull request most recent head 64b6e77. Consider uploading reports for the commit 64b6e77 to get more accurate results

@@            Coverage Diff             @@
##           master    #1487      +/-   ##
==========================================
+ Coverage   70.42%   70.63%   +0.20%     
==========================================
  Files         232      232              
  Lines       12907    12896      -11     
==========================================
+ Hits         9090     9109      +19     
+ Misses       2837     2812      -25     
+ Partials      980      975       -5     

Impacted Files	Coverage Δ
pkg/ddc/alluxio/operations/cached.go	83.33% <100.00%> (+8.86%)	⬆️
pkg/ddc/goosefs/utils.go	90.20% <0.00%> (+1.39%)	⬆️
pkg/ddc/goosefs/ufs_internal.go	68.60% <0.00%> (+2.32%)	⬆️
pkg/ddc/goosefs/metadata.go	64.28% <0.00%> (+9.89%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2727bc7...64b6e77. Read the comment docs.

[TrafalgarZZZ]

Thx for the fix! Verified with Alluxio release-2.7.2-SNAPSHOT-3714f2b (i.e. The default image used in Fluid 0.7) and it LGTM.

For cases where timeout -t is needed, I think we can patch it later.