Revert "CI: Enable the verbose mode in the mkmf.rb."

This reverts commit a832f5c.

Because there is a simpler way to enable the verbose mode by setting the
environment variable `MAKEFLAGS`.

Author: junaruga

.github/workflows/test.yml

@@ -42,11 +42,6 @@ jobs:
       - name: depends
         run:  bundle install
 
-      # Enable the verbose option in mkmf.rb to print the compiling commands.
-      - name: enable mkmf verbose
-        run:  tool/enable-mkmf-verbose
-        if: runner.os == 'Linux' || runner.os == 'macOS'
-
       - name: compile
         run:  rake compile -- --enable-debug
 
@@ -134,10 +129,6 @@ jobs:
       - name: depends
         run:  bundle install
 
-      - name: enable mkmf verbose
-        run:  tool/enable-mkmf-verbose
-        if: runner.os == 'Linux' || runner.os == 'macOS'
-
       - name: compile
         run:  rake compile -- --enable-debug --with-openssl-dir=$HOME/.openssl/${{ matrix.openssl }}