chore: rm src/lake/lakefile.toml (#10580)

This file is essentially just for me and can cause problems with the
language server, so I have removed it from the committed code (and left
an ignored version on my own setup).

src/lake/lakefile.toml

@@ -1,12 +0,0 @@
-name = "lake"
-defaultTargets = ["Lake", "lake"]
-
-[[lean_lib]]
-name = "Lake"
-defaultFacets = ["shared"]
-
-[[lean_exe]]
-name = "lake"
-root = "LakeMain"
-supportInterpreter = true
-leanOptions.experimental.module = true