Revert "[tune] implicit-anchor optimization"

[k-takata]

This reverts commit 282338f.
It seems that the commit didn't improve the performance.
Revert it to fix #100.

[codecov-io]

Codecov Report

Merging #114 into master will increase coverage by 0.29%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #114      +/-   ##
==========================================
+ Coverage   82.93%   83.22%   +0.29%     
==========================================
  Files          62       62              
  Lines       12795    12795              
==========================================
+ Hits        10611    10649      +38     
+ Misses       2184     2146      -38

Impacted Files	Coverage Δ
regcomp.c	92.21% <100%> (ø)	⬆️
regexec.c	91.13% <0%> (+0.06%)	⬆️
enc/gb18030.c	13.68% <0%> (+6.31%)	⬆️
enc/euc_tw.c	39.39% <0%> (+9.09%)	⬆️
enc/euc_kr.c	70.37% <0%> (+33.33%)	⬆️
enc/big5.c	69.44% <0%> (+36.11%)	⬆️

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[coveralls]

Coverage increased (+0.3%) to 81.343% when pulling cef834c on fix-100 into ff464e9 on master.