lib: move all UNITTEST prototypes to C files

- make extract-unit-protos handle multi-line prototypes - but they need
  to be above the implementation

- Prototypes for static functions we use in unit tests should not be in
  header files. We generate lib/unitprotos.h for this purpose

- Removed some function wrappers written for unit tests and make them
  use UNITTEST function directly.

- Renamed time2str() in the tool to timebuf() since we have the same
  name in lib/ and in unit tests they can both be used non-static in a
  build.

This reverts commit f95fadd116.

Follow-up to #21010

Closes #21014

tests/data/test1622

@@ -22,7 +22,7 @@ tool%TESTNUMBER
 
 <verify>
 <stdout>
-time2str
+timebuf
                    0 - %SP%SP%SP%SP%SP%SP%SP%SP
                    1 - 00:00:01
                    3 - 00:00:03

tests/data/test1656

@@ -3,7 +3,7 @@
 <info>
 <keywords>
 unittest
-Curl_x509_GTime2str
+GTime2str
 </keywords>
 </info>
 
@@ -13,7 +13,7 @@ Curl_x509_GTime2str
 unittest
 </features>
 <name>
-Curl_x509_GTime2str unit tests
+GTime2str unit tests
 </name>
 </client>
 </testcase>

tests/data/test1657

@@ -3,7 +3,7 @@
 <info>
 <keywords>
 unittest
-Curl_x509_getASN1Element
+getASN1Element
 </keywords>
 </info>
 
@@ -13,7 +13,7 @@ Curl_x509_getASN1Element
 unittest
 </features>
 <name>
-Curl_x509_getASN1Element unit tests
+getASN1Element unit tests
 </name>
 </client>
 </testcase>