Remove unnecessary loadNamespace() call for {rex}

[IndrajeetPatil]

cf. #1739 (comment)

[codecov-commenter]

Codecov Report

Merging #1740 (e1f51e6) into main (080613e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head e1f51e6 differs from pull request most recent head 14cd653. Consider uploading reports for the commit 14cd653 to get more accurate results

@@            Coverage Diff             @@
##             main    #1740      +/-   ##
==========================================
+ Coverage   98.84%   98.87%   +0.02%     
==========================================
  Files         107      108       +1     
  Lines        4517     4615      +98     
==========================================
+ Hits         4465     4563      +98     
  Misses         52       52              

Impacted Files	Coverage Δ
R/exclude.R	100.00% <ø> (ø)
R/expect_lint.R	100.00% <ø> (ø)
R/backport_linter.R	100.00% <100.00%> (ø)
R/extract.R	100.00% <100.00%> (ø)
R/get_source_expressions.R	94.38% <100.00%> (ø)
R/indentation_linter.R	100.00% <100.00%> (ø)
R/lint.R	97.01% <100.00%> (-0.01%)	⬇️
R/make_linter_from_regex.R	100.00% <100.00%> (ø)

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