Update supported targets in the iverilog man page.

The fpga and vhdl targets are no longer maintained, and the fpga
target is no longer built by default. So best not to advertise
them.

driver/iverilog.man.in

@@ -16,9 +16,7 @@ sourcefile
 .PP
 \fIiverilog\fP is a compiler that translates Verilog source code into
 executable programs for simulation, or other netlist formats for
-further processing. The currently supported targets are \fIvvp\fP for
-simulation, and \fIfpga\fP for synthesis. Other target
-types are added as code generators are implemented.
+further processing. The main target is \fIvvp\fP for simulation.
 
 .SH OPTIONS
 \fIiverilog\fP accepts the following options:
@@ -323,7 +321,7 @@ library or in the main design.
 
 The Icarus Verilog compiler supports a variety of targets, for
 different purposes, and the \fB\-t\fP switch is used to select the
-desired target.
+desired target. The two fully supported targets are:
 
 .TP 8
 .B null
@@ -339,19 +337,10 @@ generated code. These opcodes are also used to generate file and
 line information for procedural warning/error messages. To enable
 the debug command tracing us the trace command (trace on) from
 the vvp interactive prompt.
-.TP 8
-.B fpga
-This is a synthesis target that supports a variety of fpga devices,
-mostly by EDIF format output. The Icarus Verilog fpga code generator
-can generate complete designs or EDIF macros that can in turn be
-imported into larger designs by other tools. The \fBfpga\fP target
-implies the synthesis \fB\-S\fP flag.
-.TP 8
-.B vhdl
-This target produces a VHDL translation of the Verilog netlist. The
-output is a single file containing VHDL entities corresponding to
-the modules in the Verilog source code. Note that only a subset of
-the Verilog language is supported.  See the wiki for more information.
+
+.PP
+For other available targets, see
+.BR "<https://steveicarus.github.io/iverilog/targets>"
 
 .SH "WARNING TYPES"
 These are the types of warnings that can be selected by the \fB\-W\fP