sync package.py with upstream spack

[simonpintarelli]

Sync local package.py with spack@develop, verified using diff with spack@develop (where boost is still present):

82,88d81
<     variant(
<         "boost_filesystem",
<         default=False,
<         description="Use Boost filesystem for self-consistent field method "
<         "mini-app. Only required when the compiler does not "
<         "support std::experimental::filesystem nor std::filesystem",
<     )
110d102
< 
162d153
<     conflicts("+boost_filesystem", when="~apps")