[balsa] Fix the meson build

[Peter Bloomfield <peterb src gnome org>]

commit 4f2e267fdec825ceffe1c2ed382cfbc8a78aaea8
Author: Albrecht Dreß <albrecht dress arcor de>
Date:   Sat Jan 6 15:31:24 2018 -0500

    Fix the meson build
    
           * src/meson.build: threads.h is no more.
    
    Signed-off-by: Peter Bloomfield <PeterBloomfield bellsouth net>

 ChangeLog       |    6 ++++++
 src/meson.build |    1 -
 2 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/ChangeLog b/ChangeLog
index 3e4466f..61dafac 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2018-01-06  Albrecht Dreß <albrecht dress arcor de>
+
+       Fix the meson build
+
+       * src/meson.build: threads.h is no more.
+
 2018-01-05  Albrecht Dreß <albrecht dress arcor de>
 
        Enable multi-threaded POP3 retrieval
diff --git a/src/meson.build b/src/meson.build
index a783fbd..b9f72bd 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -64,7 +64,6 @@ balsa_base_srclist = [
   'sendmsg-window.h',
   'store-address.c',
   'store-address.h',
-  'threads.h',
   'toolbar-factory.c',
   'toolbar-factory.h',
   'toolbar-prefs.c',