Remove use of dmlc::thread_local

[hcho3]

Extracted from #285.

• Do not use dmlc/thread_local.h.
• Replace dmlc::ThreadLocalStore with treelite::ThreadLocalStore, which is a light wrapper around thread_local storage.

[codecov]

Codecov Report

Merging #291 (19671e9) into mainline (5d7d968) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             mainline     #291   +/-   ##
===========================================
  Coverage       84.78%   84.78%           
  Complexity         46       46           
===========================================
  Files             101      102    +1     
  Lines            7899     7902    +3     
  Branches           50       50           
===========================================
+ Hits             6697     6700    +3     
  Misses           1177     1177           
  Partials           25       25           

Impacted Files	Coverage Δ
include/treelite/logging.h	100.00% <ø> (ø)
src/c_api/c_api.cc	96.65% <ø> (ø)
src/c_api/c_api_common.cc	100.00% <ø> (ø)
src/c_api/c_api_error.cc	100.00% <ø> (ø)
src/c_api/c_api_runtime.cc	86.07% <ø> (ø)
include/treelite/thread_local.h	100.00% <100.00%> (ø)

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[trivialfis]

LGTM