boost: ostracize boost_system

[madebr]

Specify library name and version: boost/all

In #7290, we declared boost_system as a header-only library.
However, other libraries still link to a dummy static/shared boost_system library.

This link is unneeded, so remove boost_system from the link list.
This fixes things for people who depend on the json manifest.

Fixes #7435

@planetmarshall
Please check this

---

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[ghost]

I detected other pull requests that are modifying boost/all recipe:

• boost: Adds with_stacktrace_noop option #7503
• [boost] Apply patch to fix https://github.com/boostorg/graph/issues/268 #6132
• [boost] For Visual Studio, pass some values of settings.compiler.toolset to B2 #5119
• boost: use clang-win toolset when compiler=Visual Studio and compiler.toolset=ClangCL #4749

This message is automatically generated by https://github.com/ericLemanissier/conan-center-conflicting-prs so don't hesitate to report issues/improvements there.

[conan-center-bot]

All green in build 1 (cfbc22ab588c7ba6022d814d1128a700c4d16e6f):

• boost/1.69.0@:
  All packages built successfully! (All logs)

• boost/1.71.0@:
  All packages built successfully! (All logs)

• boost/1.70.0@:
  All packages built successfully! (All logs)

• boost/1.74.0@:
  All packages built successfully! (All logs)

• boost/1.73.0@:
  All packages built successfully! (All logs)

• boost/1.77.0@:
  All packages built successfully! (All logs)

• boost/1.75.0@:
  All packages built successfully! (All logs)

• boost/1.76.0@:
  All packages built successfully! (All logs)

• boost/1.72.0@:
  All packages built successfully! (All logs)

[planetmarshall]

Looks good to me.