Automatically remove aclocal.m4 if present

Automatically remove aclocal.m4 if present

Commit 4e7064d173d2b5b22e159fcf52d22b10213b67b8 removed the usage of
`aclocal.m4`. When using Git repositories, many times cleaning of the
generated files is not done prior to running phpize or buildconf. For
example:

  git clone git://github.com/php/php-src
  cd php-src
  git checkout PHP-7.3
  ./buildconf
  ./configure
  git checkout PHP-7.4
  ./buildconf # -> warnings
  ./configure # -> errors

To not accidentally include `aclocal.m4` file in the generated configure
this enhances build system experience a bit more by removing aclocal.m4
file prior to start building configure file using phpize or buildconf.