Remove regression tests' CREATE FUNCTION commands for unused C functions.

I removed these functions altogether in HEAD, in commit db3af9feb, and
it emerges that that causes trouble for cross-branch upgrade testing.
We could put back stub functions but that seems pretty silly.  Instead,
back-patch a minimal subset of db3af9feb, namely just removing the
CREATE FUNCTION commands.

Discussion: https://postgr.es/m/11927.1519756619@sss.pgh.pa.us

src/test/regress/input/create_function_1.source

@@ -37,11 +37,6 @@ CREATE FUNCTION autoinc ()
 	AS '@libdir@/autoinc@DLSUFFIX@'
 	LANGUAGE C;
 
-CREATE FUNCTION funny_dup17 ()
-        RETURNS trigger
-        AS '@libdir@/regress@DLSUFFIX@'
-        LANGUAGE C;
-
 CREATE FUNCTION trigger_return_old ()
         RETURNS trigger
         AS '@libdir@/regress@DLSUFFIX@'

src/test/regress/input/create_function_2.source

@@ -72,11 +72,6 @@ CREATE FUNCTION overpaid(emp)
    AS '@libdir@/regress@DLSUFFIX@'
    LANGUAGE C STRICT;
 
-CREATE FUNCTION boxarea(box)
-   RETURNS float8
-   AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
-
 CREATE FUNCTION interpt_pp(path, path)
    RETURNS point
    AS '@libdir@/regress@DLSUFFIX@'

src/test/regress/output/create_function_1.source

@@ -35,10 +35,6 @@ CREATE FUNCTION autoinc ()
 	RETURNS trigger
 	AS '@libdir@/autoinc@DLSUFFIX@'
 	LANGUAGE C;
-CREATE FUNCTION funny_dup17 ()
-        RETURNS trigger
-        AS '@libdir@/regress@DLSUFFIX@'
-        LANGUAGE C;
 CREATE FUNCTION trigger_return_old ()
         RETURNS trigger
         AS '@libdir@/regress@DLSUFFIX@'

src/test/regress/output/create_function_2.source

@@ -55,10 +55,6 @@ CREATE FUNCTION overpaid(emp)
    RETURNS bool
    AS '@libdir@/regress@DLSUFFIX@'
    LANGUAGE C STRICT;
-CREATE FUNCTION boxarea(box)
-   RETURNS float8
-   AS '@libdir@/regress@DLSUFFIX@'
-   LANGUAGE C STRICT;
 CREATE FUNCTION interpt_pp(path, path)
    RETURNS point
    AS '@libdir@/regress@DLSUFFIX@'