Merge pull request #1642 from ibuclaw/extern-cpp

grammar: Remove dangling closing parenthesis
merged-on-behalf-of: Rainer Schuetze <rainers@users.noreply.github.com>

Author: dlang-bot

spec/grammar.dd

@@ -1626,7 +1626,6 @@ $(GNAME LinkageType):
     $(D Pascal)
     $(D System)
     $(D Objective-C)
-)
 
 $(GNAME CppAggregateType):
     $(D class)