Remove snapcraft.yaml.

Removing explicit snapcraft support from janet. Getting things working
with snapcraft is not something I have had luck with, and snapcraft.io
has been spamming me with emails. Since this is not completely zero
overhead, I am simply removing support for snapcraft.

snapcraft.yaml

@@ -1,27 +0,0 @@
-name: janet
-adopt-info: janet
-summary: functional and imperative programming language and bytecode interpreter
-description: |
-    **Janet** is a functional and imperative programming language and bytecode interpreter. It is a
-    Lisp-like language, but lists are replaced
-    by other data structures (arrays, tables (hash table), struct (immutable hash table), tuples).
-    The language also supports bridging to native code written in C, meta-programming with macros, and bytecode assembly.
-base: core18
-confinement: classic
-grade: stable
-apps:
-    janet:
-        command: usr/bin/janet
-        adapter: none
-    jpm:
-        command: usr/bin/jpm
-        adapter: none
-parts:
-    janet:
-        plugin: make
-        source: .
-        make-parameters: [PREFIX=/usr]
-        build-packages: [build-essential]
-        override-build: |
-            snapcraftctl build
-            snapcraftctl set-version "$($SNAPCRAFT_PART_INSTALL/usr/bin/janet -e '(print "Version: " janet/version)' | awk '{ print $2 }')"