Remove spurious exit() calls from configure.ac

We added these a while ago, but they do no actual good, and
cause implicit declaration warnings in some situations.  Rather than
just adding stdint.h, it's easier to remove the exit() calls
as redundant.

Fixes bug 18626; bugfix from "cypherpunks"

changes/bug18626

@@ -0,0 +1,5 @@
+  o Minor bugfixes (build):
+    - Avoid spurious failures from configure files related
+      to calling exit(0) in TOR_SEARCH_LIBRARY.
+      Fixes bug 18625; bugfix on 0.2.0.1-alpha.
+      Patch from "cypherpunks".