Drop the nim grammar and refresh language counts

Removes the heaviest vendored grammar (66 MB) along with its language
wiring and test fixtures; the supported-language count moves to 158
across README, site, and manifest. The grammar manifest additionally
records the canonical-source decisions for the five
registry-disagreement grammars and the per-directory license files
restored earlier this week.

src/discover/language.c

@@ -461,10 +461,8 @@ static const ext_entry_t EXT_TABLE[] = {
     {".ncl", CBM_LANG_NICKEL},
 
     /* Nim */
-    {".nim", CBM_LANG_NIM},
 
     /* Nim */
-    {".nims", CBM_LANG_NIM},
 
     /* Squirrel */
     {".nut", CBM_LANG_SQUIRREL},