Eliminate EnvList from mutt/filter.c

[flatcap]

mutt/filter.c relies on EnvList in globals.h.
It's used in filter_create_fd() which is used by filter_create() and 19 other functions.

Source: gv svg
Key:

• Red - functions in libmutt
• Blue - functions in other libraries

The solution's probably to add an envlist param to these callers.

Currently EnvList lives in globals.c in the large mass of undifferentiated code in the root dir.
Perhaps the next step might be to move it to libcore.
Suggestions welcome.

[flatcap]

Completed in: 568ff1c remove global EnvList from mutt/filter.c
libmutt is now dep-free.