Eliminate the perl.gprof and perl.gcov Makefile targets.

Eliminate the perl.gprof and perl.gcov Makefile targets.

I don't feel that it's worthwhile having specific named targets for
building named binaries for use with gprof and gcov given that one has to
(re)Configure with the appropriate C compiler flags, hence all the object
files and the F<perl> that the build tree would build are just as enabled
(or contaminated) with profiling code as the specially named binary.

Update the documentation on using gprof and gcov to reflect that the binary
named F<perl> is now the binary that is profiled.